staylor761

i have an 08 a4 but not sure if its b7 or b8

audi8k

An easy way to separate B8 from B7 is to look at the door sides in the photos:
https://en.wikipedia.org/wiki/Audi_A4

SMac770

If you have your PR sticker in your service manual, it should say Type 8E (B6/B7) or 8K (B8).
It's also in the VIN, but not sure if UK VINs are formatted like US VINs (7th and 8th character).
But it should also be pretty obvious from the front and rear views of the car which it is. The headlights, bumper, taillights, and rear trunk/gate design are all distinct.