1. A pharmaceutical composition, comprising a thiazolidinedione, such as Compound (I), metformin hydrochloride and a pharmaceutically acceptable carrier, wherein the thiazolidinedione and metformin hydrochloride are each dispersed within its own pharmaceutically acceptable carrier in the pharmaceutical composition. 2. A composition according to claim 1, wherein the carrier for the thiazolidinedione, is different in composition to that of the carrier for metformin hydrochloride. 3. A composition according to claim 1 or claim 2, wherein the thiazolidinedione and its carrier are substantially in admixture with the metformin hydrochloride and its carrier. 4. A composition according to any one of claims 1 to 3, wherein the thiazolidinedione and its carrier are substantially in homogenous admixture with the metformin hydrochloride and its carrier. 5. A composition according to any one of claims 1 to 4, wherein the thiazolidinedione/carrier mixture is compacted with the metformin hydrochloride/carrier mixture in the composition. 6. A composition according to any one of claims 1 to 5, wherein the composition is in the form of a tablet. 7. A composition according to any one of claims 1 to 6, wherein the carrier for the thiazolidinedione comprises one or more components selected from: a binding agent other than PVP, a filler, a lubricants, a glidant, a disintegrant and a wetting agent. 8. A composition according to any one of claims 1 to 7, wherein the carrier for the metformin hydrochloride comprises one or more components selected from: a binding agent being PVP, a filler, a lubricants, a glidant, a disintegrant and a wetting agent. 9. A composition according to claim 8, wherein the carrier for the metformin hydrochloride comprises at least one additional binder. 10. A composition according to claim 9, wherein the amount of PVP is the minimum required to provide the required compressibility for metformin. 11. A composition according to claim 1, wherein the thiazolidinedione and metformin hydrochloride are located in discrete zones with respect to each other and wherein each zone comprises the active agent and optionally a carrier. 12. A composition according to claim 11, each zone is a compressed layer. 13. A composition according to claim 11 or 12, in the form of a multilayer tablet, wherein the active agents are in separate layers. 14. A composition according to any one of claims 11 to 13, wherein the discrete zones are separated by a barrier layer. 15. A composition according to claim 13, wherein the barrier layer comprises a filler, and a lubricant. 16. A composition according to claim 11, wherein one zone is a compressed layer and the other is in a powder form. 17. A composition according to claim 16, wherein the compressed layer is a tablet and the tablet and powder are encapsulated in a capsule form. 18. A composition according to any one of claims 1 to 17, wherein thiazolidinedione is selected from: Compound (I) or include (+)-5-[[4-[(3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-yl)methoxy]phenyl]methyl]-2,4-thiazolidinedione (or troglitazone), 5-[4-[(1-methylcyclohexyl)methoxylbenzyl]thiazolidine-2,4-dione (or ciglitazone), 5-[4-[2-(5-ethylpyridin-2-yl)ethoxy]benzyl]thiazolidine-2,4-dione (or pioglitazone) or 5-[(2-benzyl-2,3-dihydrobenzopyran)-5-ylmethyl) thiazolidine-2,4-dione (or englitazone), especially 5-[4-[2-(5-ethylpyridin-2-yl)ethoxy]benzyl]thiazolidine-2,4dione (or pioglitazone). 19. A composition according to any one of claims 1 to 19, wherein the composition comprises 2 to 12 mg of Compound (I). 20. A composition according to any one of claims 1 to 19, wherein the composition comprises 100 to 3000 mg of metformin hydrochloride. 21. A process for preparing a pharmaceutical composition according to claim 1, comprising a thiazolidinedione and metformin hydrochloride which process comprises: (a) for a composition wherein the thiazolidinedione and metformin hydrochloride are each dispersed within its own pharmaceutically acceptable carrier, (i) admixing the thiazolidinedione and a pharmaceutically acceptable carrier; (ii) admixing the metformin hydrochloride and a pharmaceutically acceptable carrier; and (iii) formulating the thiazolidinedione/pharmaceutically acceptable carrier mixture with the metformin hydrochloride/pharmaceutically acceptable carrier mixture or (b) for a composition wherein the thiazolidinedione and the metformin hydrochloride are located in discrete zones with respect to each other, step (iii) of the above process, comprises formulating the thiazolidinedione/carrier mixture and the metformin hydrochloride/carrier mixture into discrete zones with respect to each other.