Hm, sounds like a pain. The thing to do is to get clear in your head what your rights are, the dealer will always try to push the issue elsewhere (at least usually!).
I'm not sure how long you;'ve had the car but you may still be within the time period you can threaten to reject the car, it's probably worth getting a few form letters from around the 'net ready, just on the off chance.
Depending on how it goes, I would consider doing a letter that clearly states the main facts, when you got the car, how long after the issues became apparent, what those issues are, when you notified the dealer and what you expect them to do about it.
You may be lucky and they take ownership of it, I guess it's a "prepare for the worst, hope for the best" situation.
I've rejected a car once, it was stressful I won't lie, this was from a main dealer and they squirmed as much as they possibly could, despite BMW's much-vaunted "1000 mile return policy". the key thing is (I think) is to make sure they know you're not going to be fobbed off and go away.
Good luck with it, post back how you get on? the main thing to bear in mind is, the law is on your side at this stage of the game, so use it to best effect, go to citizens advice if need be, but don't allow the dealer to delay things.