Verifying AS results

As part of my offer conditions, Warwick have asked me to get my A level results verified.

I have all my certificates but I only have my grade slips for my AS results (I don't think our school cashed in our AS's). Will it be enough to get the grade slip photocopied, signed and stamped? Or would I need to purchase a certificate from the exam board?

By AS levels do you mean ones that you took to A2 and did the full A-level or ones you dropped?

The AS subject which I dropped. I'm going to email Warwick and check with my old sixth form to see what they say, but thank you for the advice.

I sort of assumed grade slips would be fine since a lot of schools don't cash in AS levels, so a lot of people enrolling wouldn't have certificates...pretty poor reasoning, I know!