Hang on, let's go back here. I can guess at some of the answers, but let's get them clarified in one place anyway.
When did you buy the car? From a dealer, yes? Mileage & year? What price did you pay? (Yes, this is all relevant to the naysayers!).
When did you notice the problem? When did you let them know there was an issue? What did they do when you told them? Are they declining to fix unless you cough up?
My initial thoughts are that this has SOGA and SCC written all over it. 2 months is nothing, a court is very likely likely to agree that the fault existed from purchase. They can fit whatever parts they like to solve the problem, they do NOT have to use OEM parts, but they DO have to fix it. Wear and tear isn't relevant at this point AS LONG AS THE MILEAGE ISNT SKY HIGH. I agree with Alex, £350 is peanuts if the car is on the original clutch and flywheel, so take that. If it doesn't fix the problem, so what? They have to take it back and fix it again, not your problem and not your cost.