You noticed the clutch issues on the test drive, that would have been the time to agree the purchase of the car once the problem was rectified, not before.

I'll leave it to others how you go about rejecting the vehicle if thats what you wish, in the meantime if you have a friendly indy you've used before you could ask them for second opinion (it could after all be a broken engine mounting) and a quote for a new clutch if that is indeed the issue, then when you have a ball park figure but still wish to keep the vehicle negotiate something with the seller, maybe along the lines of them fitting a new complete clutch but spltting the costs.

It's actually been well maintained with regular services and no major issues on MOTs, just the usual brake pad changes and suspension bits and pieces and only minimal surface rust under the body which is why I thought it was a good deal for me.

In terms of warranty it came with 3 months warranty, but my main issue is that there was no mention of a potential clutch/DMF problem and was described as being in an "excellent, well maintained condition" so I don't think it would be unfair to to assume it should have been in working order and any potential problems should have been noted in the advert. Also only admitting there seems to be a problem after the sale seems a little bit slippery.

You have bought a car in what sounds like very good condition for its advanced age - many of its contemporaries will already be sorap, In the real world it is naive to expect a trader to advertise, or even know about, a mechanical tremor when driving, and also to expect to reject a car of that age with what sounds like a pretty normal (and moderate) wear and tear symptom. I still think you should accept its good condition and probably spend a bit more to extend its life. Your warranty will not cover much to your advantage, and you could possibly have waived it and haggled the price down !