FORM -2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See Section 10) LAUNDRY DETERGENT COMPOSITIONS HINDUSTAN LEVER LIMITED, a company incorporated under the Indian Companies Act, 1913 and having its registered office at Hindustan Lever House, 165/166, Backbay Reclamation, Mumbai -400 020, Maharashtra, India GRANTED following specification particularly describes the nature of the invention and the manner in which it is to be performed. 1-9-2004 DETERGENT COMPOSITIONS TECHNICAL FIELD 5 The present invention relates to laundry detergent compositions giving especial benefits in the laundering of white fabrics. The compositions of the invention, which contain a combination of two different sequestrants, have 10 been found to give improved maintenance of colour fidelity, especially of white and light-coloured fabrics, during the. wash. 15 BACKGROUND In some countries the water supply contains a relatively high concentration of iron and this can lead to the discolouration (yellowing) of white and light-coloured 20 fabrics on laundering due to the deposition of Fe(III) salts. This changes the appearance and shortens the useful life of the articles. WO 00/34427A (Unilever) discloses and claims non-bleaching 25 laundry detergent compositions containing from 0.05 to 2.5 wt% of the sequestrant, iminodisuccinate (IDS) or hydroxyiminodisuccinate (HIDS). The compositions provides improved maintenance and/or restoration of colour fidelity during the wash, especially at low wash pH. 30 IDS is known as a detergency builder from US 3 697 453 (Pfizer) and EP 757 094A (Bayer) . IDS as a bleach stabiliser is disclosed in EP 509 382A (W R Grace & Co/Hampshire Chemical Corporation) and WO 97 20907A (Procter & Gamble). US 5 318 726 (Henkel) discloses HIDS as a bleach stabiliser in detergent compositions, comparable in effectiveness to diethylenetriamine pentamethylene phosphonate. DE 43311440 (Henkel) discloses HIDS with citrate or other polycarboxylates or polymeric polycarboxylates. It has now been found that synergistic maintenance of whiteness or colour fidelity may be observed if IDS or HIDS is used in combination with a second compound capable of sequestering heavy metal ions. In particular, the second sequestrant may be a water-soluble polymer containing specified aminocarboxylic structural units, or a so-called "surfactant sequestrant", or sodium glucoheptonate. EP 802 177A (Nippon Shokubai) discloses water-soluble aminocarboxylic monomers which are condensation products of an amino acid with a dicarboxylic acid anhydride, for example aspartic acid/maleic anhydride, and homo- and copolymers thereof. Copolymers of these monomers with acrylic acid and/or maleic acid exhibit excellent chelating and dispersing properties and may be incorporated in detergent compositions. Magnesium glucoheptonate as a laundry detergent ingredient is disclosed in GB 2 016 540A (Rhone-Poulenc). Peroxyacid bleach particles containing glucoheptonate are disclosed in WO 96 11252A (Eka Nobel AB). The use of sodium glucoheptonate in compositions for hard surface cleaning is disclosed in US 3 956 157 (W R Grace), EP 844 301A (Unilever), GB 2 068 405A (Sandoz). EP 757 094A (Bayer) discloses detergent and cleaning compositions containing iminodisuccinates, and also containing polymers containing succinyl units. A specific example contains 23 wt% of tetrasodium iminodisuccinate and 6 wt% of sodium polyaspertate of molecular weight 3000. DEFINITION OF THE INVENTION The present invention provides a laundry detergent composition comprising surfactant, builder, optionally other detergent ingredients, and: (a) from 0.05 to 2.5 wt% of a first sequestrant of Fe (III) ions which is a compound of the formula I: wherein Y is H or OH, and each X is individually H or a solubilising cation, characterized in that it further comprises: (b) from 0.01 to 2.5 wt% of a second sequestrant of Fe (III) ions selected from (b) (i) water-soluble polymers comprising structural units of the formula II: wherein R1 is H or COOX, preferably COOX ; R2 is H or CH2COOX but R1 and R2 cannot both be H, and R2 is preferably H; R3 is COOX, OH or CH2COOX, preferably COOX; and each X is individually H or a solubilising cation ; (b) (ii) surfactant sequestrants of the formula III : wherein R4 is a C8 to C18 alkyl group, preferably a C12-C14 alkyl group, and each X individually is H or a solubilising cation ; and (b) (iii) compounds of the formula IV : HO - CH2 - (CH-OH)5 - COOX (IV) wherein X is H or a solubilising cation. A further subject of the invention is a method of protecting new white or light-coloured textile fabrics form colour degradation on laundering, which comprises laundering the fabrics by hand or machine in a wash liquor containing a detergent composition as defined above. A further subject of the invention is the use of a compound of the formula I above in combination with a second sequestrant for di- and polyvalent metal ions in a laundry detergent composition to protect new white or light-coloured 5 textile fabrics from colour degradation on laundering. The term "colour fidelity" is used herein to include both the true colour of coloured fabrics and the whiteness of white fabrics. The benefits of the present invention are 10 especially applicable to white or light-coloured fabrics where iron deposition will cause the greatest deterioration in appearance. 15 DETAILED DESCRIPTION OF THE INVENTION The compound of formula I The detergent compositions of the invention contain, as an 20 essential ingredient, a compound of the formula I: 25 wherein Y is H or OH, preferably H; and X is H or a solubilising cation, preferably a sodium ion. If Y is a hydrogen atom, the formula I represents 30 iminodisuccinic acid or a water-soluble salt thereof. Iminodisuccinic acid, also known as N-(1, 2-carboxyethyl)D,L-aspartic acid, has the formula (Ia) wherein X = H: 1 5 In the following description, the abbreviation "IDS" will be used to denote this material whether in acid or salt form. IDS is commercially available from Bayer AG, Leverkusen, 10 Germany, and from Nippon Shokubai KK, Japan. If Y is a hydroxyl group, the formula I represents hydroxyiminodisuccinic acid or a water-soluble salt thereof. 15 Hydroxyiminodisuccinic acid has the formula (lb) wherein X = H: 20 In the following description, the abbreviation "HIDS" will 25 be used to denote this material whether in acid or salt form. HIDS is commercially available from Nippon Shokubai KK, Japan. For the purposes of the present invention, the IDS or HIDS 30 may be, and preferably is, in the form of a salt, ie X in the formula I is a stable solubilising cation, preferably an alkali metal cation, more preferably sodium. In the laundry detergent compositions of the invention, IDS 35 or HIDS is suitably present in an amount of from 0.05 to 2.5 wt%, preferably from 0.2 to 2.5 wt%, more preferably from 0.3 to 1.5 wt%. 5 The second sequestrant The compositions of the invention also contain a second compound which is a sequestrant of di- and polyvalent metal ions. 10 The optimum amount of the second sequestrant present will depend on the choice of sequestrant, and may range, for example from 0.01 to 2.5 wt%. 15 Three preferred classes of second sequestrant are envisaged. Preferred Embodiment (i) 20 According to a first preferred embodiment of the invention, the second sequestrant is a a water-soluble polymer comprising structural units of the formula II 25 30 wherein R1 is H or COOX, R2 is H or CH2COOX but R1 and R2 cannot both be H, R3 is COOX, OH or CH2COOX, and each X is individually H or a solubilising cation. 5 These polymers are described and claimed in EP 802 177A (Nippon Shokubai), which describes and claims also the monomers from which they are derived, and detergent compositions containing the polymers. 10 The aminocarboxylic monomers from which the structural units of the formula II are derived are condensation products of an amino acid, for example, aspartic acid, serine or glutamic acid with the anhydride of an unsaturated 15 dicarboxylic acid, for example, maleic anhydride, itaconic anhydride or aconitic anhydride. An especially preferred monomer is the condensation product of aspartic acid with maleic anhydride, giving in the polymer structural units of the formula II in which R1 is COOX, R2 is H and R3 is COOX. 20 The water-soluble polymers may be homo- or copolymers. Especially preferred are copolymers comprising at least 15 mole%, preferably at least 20 mole%, of structural units of the formula II. The copolymers may further comprise 25 structural units of unsaturated mono- or dicarboxylic acids. Preferred copolymers contain structural units of maleic acid and/or acrylic acid. Preferred copolymers comprise from 15 to 50 mole% of 30 structural units of the formula II, from 50 to 85 mole% of structural units of acrylic acid, and optionally from 0 to 15 mole% of structural units of maleic acid. Especially preferred are terpolymers comprising from 2 0 to 3 0 mole% of structural units of the formula II, from 60 to 80. mole% of structural units of acrylic acid, and from 1 to 10 mole% of structural units of maleic acid. 5 An especially preferred polymer contains 25 mole% of structural units of a condensation product of aspartic acid and maleic anhydride (MA-Asp), 5 mole% of maleic acid (MA) units, and 70 mole% of acrylic acid (AA) units. This 10 polymer will be referred to hereinafter as a MA-Asp/MA/AA terpolymer. The polymer suitably has a weight average molecular weight of from 800 to 8 million, preferably from 1000 to 100 000. 15 Polymers having a weight average molecular weight of 2 000 to 10 000 are preferred. The polymer may suitably be present in the composition in the invention in an amount of from 0.01 to 2 wt%, more 20 preferably from 0.02 to 1 wt% and most preferably from 0.02 to 0.5 wt%. Preferred embodiment (ii) 25 According to a second preferred embodiment of the invention, the second sequestrant is "surfactant sequestrant", that is to say, a sequestrant molecule that includes a hydrophobic moiety, for example, a long-chain alkyl group. Examples of surfactant seguestrants are aminopolycarboxylates containing at least three carboxyl groups, and a C8-Ci8 alkyl chain. 5 A preferred surfactant sequestrant is a compound -of the formula III CH2 - COOX I N - CH2 - COOX (III) 10 | CH - COOX I R4 15 wherein R4 is a C8 to C18 alkyl group, preferably a C12-C14 alkyl group, and each X individually is H or a solubilising cation. This compound, alkylglycine diacetic acid, will be referred to hereinafter as AGDA. AGDA. is commercially available from BASF AG, Germany. 20 AGDA or other surfactant sequestrant may suitably be present in the compositions of the invention in an amount of from 0.05 to 2.5 wt%, preferably from 0.1 to 2.0 wt%. 25 Preferred embodiment (iii) According to a third preferred embodiment of the invention, the second sequestrant is a compound of the formula IV 30 HO - CH2 - (CH-OH)5 - COOX (IV) wherein X is H or a solubilising cation. This compound is a glucoheptonate. Glucoheptonate, preferably sodium glucoheptonate, may suitably be present in an amount of from 0.01 to 2 wt%, 5 preferably from 0.02 to 1 wt%. Detergent compositions 10 The composition of the invention also contains other conventional detergent ingredients. Essential ingredients are surfactants (detergent-active compounds) and detergency builders, and other conventional ingredients may optionally be present. 15 Detergent compositions of the invention may suitably comprise from 5 to 60 wt% of one or more detergent surfactants and from 10 to 80 wt% of one or more detergency *-■ i builders, as well as the preferred amounts of the first and 20 second sequestrants, and optionally other detergent ingredients to 100 wt%. According to one preferred embodiment of the invention, the compositions of the invention may be substantially free of 25 bleaching ingredients. Detergent ingredients 30 The detergent compositions will contain, as essential ingredients, one or more detergent active compounds (surfactants) which may be chosen from soap and non-soap anionic, cationic, nonionic, amphoteric and zwitterionic detergent active compounds, and mixtures thereof. Many suitable detergent active compounds are available and are fully described in the literature, for example, in 5 "Surface-Active Agents and Detergents", Volumes