Okay I've just had a talk with the local dealer & the nice lady quoted me £628 for Belt kit & Water pump! then she took my Reg number to double check & said my car doesn't have a belt, apparently it's chain driven!
Win!!! ...I thought. Now I'd previously called Russell Automotive and they've quoted me £490 for belt kit (including tensioner) and water pump, which seems ...exploitative, considering I didn't know it was chain driven at the time.
I asked Audi service how much for just the Water Pump change & she quoted me
£628 ...

...she said it's because there was a special offer on for the Belt kit, but the Water pump alone didn't qualify for the discount! I told her I'd call back & hung up in shock.
I've yet to call Russells back for a new quote as it's all still sinking in.
Moral: book a belt change ...even if you don't have one.