Compounds Useful in Therapy This invention relates to novel compounds, and their derivatives., which are useful in therapy and to processes for their preparation. It also relates to Intermediates used in the preparation of such compounds and derivatives, compositions containing them and their uses. Endometriosis is a common gynaecological disease that affects 10-20% women of reproductive age and manifests itself in the presence of functional ectopic endometrial glands and stroma at locations outside the uterine cavity {Prentice, A. (2001). Bmj 323, 93-95.}. Patients with endometriosis may present with many different symptoms and severity. Most commonly this is dysmetionrhpea, but chronic pelvic pain, dyspareunia, dyschexia, monorrhagia, lower abdominal or back pain, infertility, Moating and pain on micturition are also part of the constellation of symptoms of endometriosis. Originally described by Von Rokttansky in 1860 {Von Rokttansky, C. (1860). Ztsch K K Gesellsch der Aerzte zu Wien 37, 577-581.}, the exact pathogenesis of endometriosis is unclear {Wltz, C. A. (1999). Clinical Obstetrics & Gynaecology 42, 566-585.; Wltz, C. A. (2002). Gynaecologic & Obstetric Investigation 53, 52-62.}, but the most widely accepted theory is the implantation, or Sampson, theory {Sampson, J. A. (1927). American Journal of Obstetrics & Gynaecology 14, 422-429.}. The Sampson theory proposes that the development of endometriosis is a consequence of retrograde dissemination and implantation of endometrial. .tissue into the peritoneal cavity during menstruation. Following attachment, the fragments of endometrium recruit a vascular supply and undergo cycles of proliferation and shedding under local arid systemic hormonal controls. In women with patent fallopian tubes, retrograde menstruation appears to be a universal phenomenon {Liu, D. T. (Hitchcock, A.). British Journal! of Obstetrics & Gynaecology 93, 859-862.}. The disease often manifests itself as rectovaginal endometriosis or adenomyosis, ovarian cystic endometriomas and, most commonly, peritoneal endometriosis. The major sites of attachment and lesion growth within the pelvis are the ovaries, broad and round ligaments, fallopian lubes, cervix, vagina, peritoneum and the pouch of Douglas. At its most severe, endometriosis can cause profound structural modification to peritoneal cavity, including mufti-organ adhesions and fibrosis. Symptomatic endometriosis can be managed medically and surgically, where the intention is to remove the ectopic lesion tissue. Surgical intervention can be either conservative, aiming to preserve the reproductive potential of the patient, or comparatfvely radlcaT for severe disease, involving dissection of the urinary tract, bowel, and rectovaginal septum, or total abdominal hysterectomy and bilateral salpuigo-oopherectomy. Medical pharmacological treatments such as the androgenic therapies, danazol and gestrinone, the constellation of GnRH agonists, busereiin, gosereljn, leuprolide, nafarelin and triptorelin, GnRH antagonists, cetrorelix and abarelix, as well as the progestogens, including medroxyprogesterone acetate, induce lesion atrophy by suppressing the production of estrogen. These approaches are not without unwanted side effects; danazol and gestrinone include weight gain, hirsuitism, acne, mood changes and metabolic effects on the cardiovascular system. The group of GnRH agonists and antagonists are found to cause a profound suppression of estrogen leading to vasomotor effects {hot flashes) and depletion of bone mineral density, which restricts their use to only six months of therapy. The group of progestogens, including medroxyprogesterone acetate, suppress the gonadotropins, but do not down-regulate ovarian estrogen production to the same extent as the GnRH analogues. The side effects include irregular bleeding, bloating, weight gain and metabolic effects on the cardiovascular system. Uterine leiomyomas {Flake, G. P., et al. (2003). Environmental Health Perspectives 1'11, 1037-1064.; Walker, C. L. (2002). Recent Progress in Hormone Research 57, 277-294.}, or fibroids, are the most common benign tumours found in women and occur in the majority of women by the time they reach the menopause. Although uterine fibroids are the most frequent indication for hysterectomy in the United States, as with endometriosis, remarkably little is known about the underlying pathophysiology of the disease. As with endometriotic lesions, the presence of enlarged uterine fibroids is associated with abnormal uterine bleeding, dysmenorthoea, pelvic pain and infertility. Outside of surgical management, medical treatments commonly used for endometriosis, such as GnRH analogues or danazol, have been shown to suppress fibroid growth by inducing a reversible hypoestrogenfc state {Chrisp, P., and Goa, K. L (1990). Drugs 39, 523-551.; Chrisp, P., and Goa, K. L. (1991). Drugs 41, 264-28B.; De Leo, V., et al. (2002). Drug Safely 25, 759-779.; ishmara, H., et aJ. (2003). Fertility & Sterility 79, 735-742.}. However, the future disease management of both uterine fibroids and endometriosis will rely on the development of more effective, well-toterated and safer agents than those that are currently available. Steroidal progestins (i.e., progesterone receptor agonists) are commonly used in women's health, such as in contraception and hormone therapy and for the treatment of gynecological disorders. Recent studies in women and in nonhuman primates also indicate that progesterone receptor antagonists may have potential applications in contraception and for the treatment of reproductive disorders such as fibroids and endometriosis. Currently, all clinically available progesterone receptor agonists and antagonists are steroidal compounds. They often cause various side effects due to their functional interactions with other steroid receptors or because of effects associated with their steroidal metabolites (Winneker, Richard C. et al.; Endocrinology and Reproductive Disorders Division, Women's Health Research institute, Collegevilte, PA, USA. Seminars in Reproductive Medicine (2005), 23(1), 46-57). Progesterone receptor antagonists [anti-progestins (APs)], including the founding members the class mifepristone (RU-486; Roussel UCLAF, Romainville, France), onapristone (ZK 98 299; Schering AG), 2K 137 316 and ZK-230 211, are compounds that bind to the progesterone receptor (PR) and prevent progesterone-induced gene expression {Spitz, I. M. (2003). Steroids 68, 981-993.}. Acting on the estrogen primed endometrium, progesterone pfays an essential role in the differentiation and ductal morphogenesis of endometrial tissue, but also participates in the inhibition of myometrial contractility and the polarisation of leukocyte Tb1/Th2 responses that are critical for embryo implantation and the maintenance of pregnancy. A number of studies have investigated the potential beneficial effects of anti-progestins on the signs and symptoms of endometriosis {Grow, D. R., et al. (1996). Journal of Clinical Endocrinology & Metabolism 81, 1933-1939.; Kettel, L M., et at. (1996). Fertility & Sterility 65, 23-28.; Kettel, L. M., et at. (1998). American Journal of Obstetrics & Gynaecology 178, 1151-1156.} and uterine fibroids {Eisinger, S. H., et a!. (2003). Obstetrics & Gynaecology 101, 243-250.; Murphy, A. A., and Castellano, P. Z. (1994). Current Opintion in Obstetrics & Gynaecology 6, 269-278.; Murphy, A. A., et at. (1995). Fertlity & Sterility 63, 761-766.; Steinauer, J., Pritts, et aL (2004). Obstetrics & Gynaecology 103, 1331-1336.; Yang, Y., et al. (1996). Chinese. Chung-Hua Fu Chan Ko Tsa Chlh [Chinese Journal of Obstetrics & Gynaecology] 31, 624-626.}. Unlike GnRH analogues, and other conventional pharmacological approaches, anli-progestins, especially mifepristone, appear to be able to reduce lesion, or fibroid volume, whilst maintaining a tonic level of ovarian oestrogen secretion. Such anli-progestins induce amenorrhoea and endometrial compaction, and also appear to sufficiently protect against rapid oestrogen-dependent bone loss {Grow, D. R., et al. (1996). Journal of Clinical Endocrinology & Metabolism 81,1933-1939.}. In contrast GnRH analogues cause a rapid loss in bone mineral density, a clinical feature which limits their treatment duration to 6 months. Whilst mifepristone is a potent anti-progestin, it also has equipotent anti-gtuoocorticoid activity. Outside of a palliative treatment of hypercortisolism for Cushing's syndrome {Chu, J. W., et al. (2001). J Clin Endocrinol Metab 86, 3568-3573.; Sartor, O., and Cutler, G. B., Jr. (1996). Clin Obstet Gynaecol 39, 506-510.; Spitz, I. M. (2003). Steroids 68, 981-993.; Van Look, P. F. and von Hertzen, H. (1995). Human Reproduction Update 1,19-34.}, the artt'-giucocortjcoid activity is an undesirabte feature of mifepristone and potentially many of the steroidal dasses of anti-progestins. A further class of steroidal and non-steroidal compounds, termed the progesterone receptor modulators (PRMs, or mesoprogestins), induding asoprisnil (J867, benzaldehyde, 4-[(11B, 178)-17-methoxy-17-(memoxymethyl)-3-oxoestra-4,9-dien-11-yl]-, 1-oxime; Jertpharm, TAP), J912, J956, J1042, have also been described. In addition to their potential utility in hormone replacement and as contraceptives, these dasses of compounds could be considered to have utility in the treatment of endometriosis and uterine leiomyoma {Chwalisz, K., et al. (2004). Semin Reprod Med 22, 113-119.; Chwafisz, K., et al. (2002). Annals of the New York Academy of Sciences 955, 373-388; discussion 389-393.; DeMarmo, D., et at. (2003). Steroids 68,1019-1032.}. Asoprisni and structurally-related PRMs differ from anii-progestjns and progestins in animaf models, demonstrating partial progesfogenic activity in the rabbit endometrium (McPhail's test (McPhail, M. K. (1934). Journal of physiology 83, 145-156.}} and guinea pig vagina, for instance. Pre-clinical studies with asoprisinil in primates have indicated that PRMs suppress endometrial growth and, unlike the effects of progestins, endometrial ER and PR expression is not repressed {Chwalisz, K., et al. (2000). Steroids 65, 741-751.; DeManno, D., et al. (2003). Steroids 68,1019-1032.; Elger, W., et al. (2000). Steroids 65, 713-723.}. The compounds of the present invention have been found to have useful pharmaceutical properties. They may be used to treat endometriosis, uterine fibroids (leiomyomata) and menorrhagia, adenomyosis, primary and secondary dysmenorrhoea (induding symptoms of dyspareunia, dyschexia and chronic pelvic pain), chronic pelvic pain syndrome, precodous puberty, cervical ripening, contraception (emergency), breast carcinoma, ovarian carcinoma, endometrial cardnoma, prostate carcinoma, pulmonaiy carcinoma, testicular carcfnoma, gastric carcinoma, meningfoma, anxiety, premenstrual syndrome, premenstrual dysphoric disorder, alcohol abuse and reward, or Charcot-Marie-Tooth disease. Particularly of interest are the following diseases' or disorders: endometriosis, uterine fibroids Oeiomyomata), menorrhagia, adenomyosis, primary and secondary dysmenorrhea (including symptoms of dyspareunia, dyscnexia and chronic pelvic pain}, and chronic pelvic pain syndrome. In particular, the compounds and derivatives of the present Invention, exhibit activity as progesterone-receptor antagonists and may be useful for treatment where progesterone receptor antagonism is indicated. More particularly, the compounds and derivatives of the present invention may be useful for Creating endometriosis and/or uterine fibroids fleiomyomata). international Patent Application WO 02/085860 describes pyrazote derivatives of the formula: wherein R1, R2, R3 and R4 are as defined therein, which are modulators of HIV reverse transcriptase. According to the present invention there is provided a compound of the formula (I), (Formula Removed) or a pharmaceutically acceptable derivative thereof, wherein R1 and R3 independently represent H, C1-6alkyl. C3-8cycloalkyl, or halogen; Rz represents C1-6alkyl, CF3 or aryi; a represents 1 or 2; R4, R5, R7 and R8 independently represent H, C1-6alkyl, C1-6alkyloxy, CN or halogen, or R4 and R5, or R7 and Ra, together with the ring to which they are attached form an aryl or heterocyclic fused ring system; X represents C or N; Y represents CH2 or O; and R6 represents H, CN or halo, but when X represents N then Ra represents H. In the above definitions alkyl groups containing the requisite number .of carbon atoms, except where indicated, can be unbranched or branched chain. Examples include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and t-butyl. Examples of aftyloxy include methoxy, ethoxy, n-propytaxy, t-propyloxy, n-butyfoxy, i-bulyloxy, sec-butyloxy and t-butyloxy. Examples of cyctoalkyl include cycJoprapyl, cyclobutyt, cyclopentyl, cyclohexyi and cydoheptyl. The term halogen means filuoro, cfiloro, bromo or Iodo. Aryl rings included within the definition of aryl are phenyl or napthyl; Heterocycies Included within the definition of heterocyclic ring are pyrrolyl, imkfazotyt, triazolyl, thienyl, furyi, thiazolyl, oxazotyl, thiadiazolyl, oxadiazolyl, pyridinyl, pyrimidinyl, pyridazinyl, pyrazinyl, indolyl, isoindolyl, qulnoiinyl, isoquinolrnyl, benzimidazoiyi, qulnazolinyl, phthalazinyl, benzoxazotyt and quinoxaiiny!, together with partially or fully saturated versions thereof as well as azetidinyl, pyrrolidjnyl, piperidinyl, piperazinyl, homopiperazjnyl, oxazepanyl, and morphoinryl. In an embodiment of the invention R1 represents C1-6alkyl or Ca-dcycloaTkyl. In a further embodiment of the invention R2 represents C1-6alkvl. In a still further embodiment of the invention R3 represents C1-6alky! or C3-8cycloalkyl. In a further embodiment of the invention R4 represents H. In a still further embodiment of the invention R5 represents H, C1-6 alkyl, or halogen. In a further embodiment of the invention R4 and R5 together represent a phenyl or pyridinyl ring fused to the ring to which they are attached. Preferably R4 and R5 together represent a phenyl ring fused to the -ring to which they are attached. In a still further embodiment of the invention R6 represents CN. In a furtherembodiment of the invention R7 represents H, C1-6 alkyl, or halogen. In a still further embodiment of the invention R8 represents H. In a further embodiment of the invention R7 and R8 together represent a phenyl or pyridinyl ring fused to the ring to which they are attached. Preferably R7 and RB together represent a phenyr ring fused to the ring to which they are attached. In a still further embodiment of the invention Y represents O. In a farther embodiment of the invention halogen represents fluoro orchloro. Preferred compounds according to the present invention are: 4-(3,5-Dicyclopropyl-1-metr»anesulfonylrnethyl-1H-pyrazol-4-ytoxy)-benzoniirie; 4-(3,5-Dicyclopropyl-1-n^hanesulfonylmethiyl-1H-pyrazol-4-yloxy)-2-methyl-benzonitrile 4-(3,5-Dicyclopropyl-1-methanesuHbnylrnethyl-1H-pyrazol-4-yloxy)-2,6-dimelhyl-benzonitrile 2-Chtoro-4-(3,5-drcyctopropvf-1 -methanesuffonylmethyl-1 H-pyrazol-4-yloxy)-benzonitrile 4-{3,5-D icyclopropyl-1 -methanesulfonylmethyl-1 H-py razol-4-yloxy)-2-fluoro-benzonitrile; 3-chloro-4-(3,5-dlcyclopropyl-1-methaiTesu1foriylme 4-(3,5-Dicyclopropyl-1-metrianesulf6niylmethyl-1 H-pyrazol-4-yloxy)-3-flucro-benzonitrile; 4-(3,5-Dicyclopropyl-1 -methanesutfonylmethyl-1 H-pyrazol-4-yloxy)-3-methoxy-benzonilrile; 4-{3,5-Dicyclopropyl-1-mettianesurfonylmethyi-1 H-pyrazol-4-;yloxy)-naphthalene-1 -carbonitrile; 5-(3,5-Dicyclapropyl-1-methanesulfonylmethy(-1H-pyrazol-4-yloxy)-quinoline-8-carbonitrile 4-(3,5-Dicyclopropyl-1-methanesulfonylmethyl-1H-pyrazol-4-yloxy)-quinoline 4-(4-Chloro-3-fluoro-phenoxy)-3,5-dicydopropyl-1-methanesu(fonylmethy]-1H-pyrazole-l 3,5-Dicyclopropyl-4-(3,4-dlfluoro-prienoxy)-1 -mathanesulfonylmethyl-1 H-pyrazole; 3,5-Dicyclopropyl-1-methanesulfonylmethyl-4-(3,4,5-trifluoro-phenoxy)-.1H-pyrazoIei 3,5-Dicyclopropyl-4-(3t5-difluoro-phenoxy)-1 -methanesulfonylmethyH H-pyrazole; 3,5-Dicyclopropyl-1-methanesulfonv(m6thyl-4-(2,4,5-trifluoro-phenosly)-1H-pyrazole 4-(3-Cyclopropyl-1-methanesiffonylmertbyl-5-methy-1H-pyrazol-4-yloxy)-2-methyl-benzonitrile 4-(5-Cyclopropyl-1-methanesiffonylmertby-3-methyI-1H-pyrazol-4-yloxy)-2-methyl-benzonitrile 4-(3-Cyclopropyl-1-methanesiffonylmertby-5-methyl-1H-pyrazol-4-yloxy)-2,6-methyl-benzonitrile 4-(5-Cyclopropyl-1-methanesurfonylmethyl-3-methyl-1H-pyrazol-4-yloxy)-2,6-methyl-benzonitrile 4-(1 -Methanesu1fonylmethyl-3,5-cfimethyl-1 H-pyrazol-4-yloxy)-2,6-dimethyl-benzonitrile 4-{3tS-Dlethyl-1-methanesulfonylmemyl-1H-pyrazol-4-yloxy)-benzonitrile 4-(3,5-Diemyl-1 -methaneaulfonylmethy1H-pyrazol-4-yloxy)-2,6-methyl-benzonitrile 4-(3,5-Di-tenrbutyl-1-methajriesulfonylmethyl-1H-pyrazol-4-yloxy)-benzonitile 4-(3-tert-ButyH -methanesulfbnylme1hyl-5-methyl-1 H-pyrazol-4-yloxy)-berEonitrite; 4-(5-tert-Butyl-1 -methanesulfonyhmefriyl-3-methyl-l H-pyrazoi-4-yloxy)-benzcinitrite; 4-(3-Chloro-5-cydopropyl-1-methariesulfonylmethyl-1H-pyrazol-4-yloxy)-2,6-dimethyl-benzonitrile 4-(5-Chtoro-3-cydopropyl-1-methanesuIfonylmethyl-1H-pyrazol-4-yloxy)-2,6-dimethyl-benzonitrile 4-(3-tyclopropyl-1-methanesulforrylmethyl-1H-pyrazol-4-yloxy)-2,6-dimethyl-benzonitrile 4-(5-Cyclopropyl-1-methanesuifcmylnremy1-1H-pyrazol-4-yloxy)-2,6-dimethyl-benzonitrile 4-(3,5-Diethyl-1-methaneulfonylmethyt-1H-pyrazol-4-ylmethvl)-benzonitrae; 4-(3,5-Dicydopropyl-1-trifluoromethanesulfionylmethyl-1H-pyrazol-4-yloxy)-benzonitrile 4-{3,5-Dicydopropyt-1-ethanesulfonytmethyl-1H-pyrazol-4-yloxy)-benzonitrile 4-[3,5-Dicyclopropyl-1-(propane-2-sulfbnylmethyl)-1H-pyrazol-4-yloxy)-benzonitrile 4-[3,5-Drcyclop'ropyl-1-{2-methyf-propane-2--sulfbnylmethyl)-1H-pyrazol-4-yloxy)-benzonitrile 4-(1 -Benzenesulfonylmeihyl-3t5-dicyclopropyl-1 H-pyrazol-4-yloxy)-benzonitri!e; 4-(3,5-Diethyl-1 -methanesulfinylmethyl-1H-pyrazol-4-yloxy)-2,6-dimethyl-benzonitrile 4-(3,5-Diethyl-1 -methanesuiflrtylmethyl-l H-pyrazol-4-ytoxy)-2,6-dimethyl-benzonitrle; and the pharmaceuticatty acceptable derivatives thereof. The above described embodiments of the invention may be combined with one or more further embodiments such that further embodiments are provided wherein two or more variables are defined more specifically in combination. For example, within the scope of the invention is a further embodiment wherein the variables R1, R2 and L all have the more limited definitions assigned to them in the more specific embodiments described above. Ail such combinations of the more specific embodiments described and defined above are within the scope of the invention Pharmaceutically acceptable derivatives of the compounds of formula {1} according to the invention include salts, solvates, complexes, polymorphs and crystal habits thereof, prodrugs, stereoisomers, geometric isomers, tautomeric forms, and isotopic variations of compounds of formula (I). Preferably, pharmaceutically acceptable derivatives of compounds of formula (I) comprise salts, solvates, esters and amides of the compounds of formula (1). More preferably, pharmaceutically acceptable, derivatives of compounds of formula (l) are salts and solvates. The pharmaceutically acceptable salts of the compounds of formula (I) include the acid addition and base salts thereof. Suitable acid addition salts are formed from acids which form non-toxic salts. Examples include the acetate, adipate, aspartate, benzoate, besyiate, bicarbonate/carbonate, bisulphate/sulphate, borate, camsytate, citrate, cyclamats, edisytate,' esylate, formate, fumarate, gluceptate, gluconate, glucuronate, hexafluorophosphate, hibenzate, hydrochloride/chloride, hyaVobromide/bromkfe, hydroiodide/iodide, isethionate, lactate, malate, maleate, malonate, mesylate, methylsulphate, naphthylate, 2-napsylate, nicotlnate, nitrate, orotate, oxalate, patmitate, pamoate, phosphate/hydrogen phosphate/dihydrogen phosphate, pyroglutamate, saccharate, stearate, succinate, tannate, tartrate, tosylate, trifluoroacetate and xinofoate salts. Suitable base salts are formed from bases that form non-toxic salts. Examples include the aluminium, arginine, benzathine, calcium, choline, diethylamine, dtolamine, glycine, lysine, magnesium, meglumine, olamine, potassium, sodium, tromethamine and zinc salts. Hemt-salts of acids and bases may also be formed, for example, hemi-sulphate and hemicalcrum salts. For a review on suitable salts, see "Handbook of Pharmaceutical Salts: Properties, Selection, and Use" by Stahl and Wermuth (Wiley-VCH, 2002). Pharmaceutically acceptable salts of compounds of formula I may be prepared by one or more of three methods: (i) by reacting the compound of formula (I) with the desired acid or base; (ii) by removing an acid- or base-labile protecting group from a suitable precursor of the compound of formula (!) or.by ring-opening a suitable cyclic precursor, for example, a lactone or lactam, using the desired acid or base; or (iii) by converting one salt of the compound of formula (t) to another by reaction with an appropriate acid or base or by means of a suitable ion exchange column. All three reactions are typically carried out In solution. The resulting salt may precipitate out and be collected by filtration or may be recovered by evaporation of the solvent The degree of ronrsation in the-resulting salt may vary from completely ionised to almost non-ionised. The compounds of the invention may exist in a continuum of sold states ranging from fully amorphous to fully crystalline. The term 'amorphous' refers to a state in which the material lacks long range order at the molecular level and, depending upon temperature, may exhibit the physical properties of a solid or a liquid. Typically such materials do not give distinctive X-ray diffraction patterns and, while exhibiting the properties of a solid, are more formally described as a Squid. Upon heating; a change from solid to liquid properties occurs which is characterised by a change of state, typically second order ('glass transition'). The term 'crystalline' refers to a solid phase in which the material has a regular ordered internal structure at the molecular level and gives a distinctive X-ray diffraction pattern with defined peaks. Such materials when heated sufficiently will also exhibit the properties of a liquid, but the change from solid to liquid is characterised by a phase change, typically first order fmelting point"). The compounds of the invention may also exist in uneolvated and solvated forms. The term 'solvate' is used herein to describe a molecular complex comprising the compound of the invention and one or more pharmaceutical^ acceptable solvent molecules, for example, ethanol. The term 'hydrate' is employed when said solvent is water. A currently accepted classification system for organic hydrates is one that defines isolated site, channel, or metal-ion coordinated hydrates - see "Polymorphism in Pharmaceutical Solids* by K. R. Mom's (Ed. H. G. Brittain, Marcel Dekker, 1995). Isolated site hydrates are ones in which the water molecules are isolated from direct contact with each other by intervening organic molecules. In channel hydrates, the water molecules lie in lattice channels where they are next to other water molecules. In metal-ion coordinated hydrates, the water molecules are bonded to the metal ion. When the solvent or water is tightly bound, the complex wili have a well-defined stoichrometry independent of humidity. When, however, the solvent or water is weakly bound, as in channel solvates and hygroscopic compounds, the water/solvent content will be dependent on humidity and drying conditions. In such cases, non-stoichiometry win be the norm. Also included within the scope of the invention are mulfr-component complexes (other than sails and solvates) wherein the drug and at least one other component are present "n stoichiometric or non- stoichiometric amounts. Complexes of this type include daihrates {drug-host inclusion complexes) and co-crystals. The latter are typically defined as crystalline complexes of neutral molecular constituents which are bound together through rwn-covalent interactions, but could also be a complex of a neutral molecule with a salt. Co-crystals may be prepared by melt crystallisation, by recrystallisation from solvents, or by physically grinding the components together - see Chem Cornmun, 17,1889-1896, by O. Almarsson and M. J. Zaworotko (2004}. For a general review of multi-component complexes, see J Pharm Sd, 64 (8), 1269-1288, by HaleWian (August 1975). The compounds of the invention may also exist in a mesomorphic state (mesophase or liquid crystal) when subjected to suitable conditions. The mesomorphic state is intermediate between the true crystalline state and the true liquid state (either melt or solution). Mesomorphism arising as the result of a change in temperature is described as thermotropic' and that resulting from the addition of a second component, such as water or anoiher solvent, is described as 'lyotropic'. Compounds that have the potential to form lyotropic mesophases are described as 'amphiphDic' and consist of molecules which possess an ionic (such as -COO'Na+, -COOK*, or -SO3Na+) or non-Ionic (such as -N"N+(CH3)3) polar head group. For more information, see Crystals and the Potariana Microscope by N. H. Hartshome and A. Stuart, 4th Edition (Edward Arnold, 1970). Hereinafter all references to compounds of formula (1} include references to salts, solvates, multi-component complexes and liquid crystals thereof and to solvates, multi-component complexes and liquid crystals of salts thereof. As indicated above, so-caHed 'prodrugs' of the compounds of formula (I) are also within the scope of the invention. Thus certain derivatives of compounds of formula (I), which may have little or no pharmacological activity themselves, can be converted into compounds of formula I having the desired activtty, for example by hydrorytfc deavage, when administered into, or onto, the body. Such derivatives are referred to as 'prodrugs'. Further information on the use of prodrugs may be found in "Pro-drugs as Novel Delivery Systems", Vol. 14, ACS Symposium Series (T. Higuchl and W. Stella) and "Bioreversible Carriers in Drug Design", Pergamon Press, 1987 (Ed. E. B. Roche, American Pharmaceutical Association). Prodrugs in accordance with the invention can be produced by repladng appropriate functionalities present in the compounds of formula (I) with certain moieties known to those skilled in the art as 'pro-moieties' as described, for example, in "Design of Prodrugs" by H. Bundgaard (Elsevier, 1985). Some examples of prodrugs in accordance with the invention Indude (i) where the compound of formula (1) contains an alcohol functionality (-OH), an ether thereof, for example, a compound wherein the hydrogen of the alcohol functionaSty of the compound of formula (I) is replaced by (C1-C6)alkanoyloxymethyl; and fli) where the compound of formula (I) contains a primary or secondary amino functionality {-NH2 or -NHR where R # H), an amide thereof, for example, a compound wherein, as the case may be, one or both hydrogens of the amino functionality of the compound of formula (I) is/are replaced by (C1-C10}alkanoyl. Further examples of replacement groups in accordance with the foregoing examples and examples of other prodrug types may be found In the aforementioned references. Moreover, certain compounds of formula (I) may themselves act as prodrugs of other compounds of formula Also included within the scope of the invention are metabolites of compounds of formula {I), that is, compounds formed in vivo upon administration of the drug.. Thus within the scope of the invention are envisaged the metabolites of the compounds of formula (I) when formed in vivo. Compounds of formula