If it's a long belt that wraps around everything, it's called a serpentine belt. If there are a couple of different belts, then it'll just be the power steering belt. As Malc says, taking the belt to any parts store i.e. motorist discount centre / eurocarparts etc. should allow them to match it up to something. Alternatively John Woolfe Racing, American Auto Parts etc. are all UK based and normally have them on the shelf if you tell them the make model and or VIN number.
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