There have been many threads on other forums on this subject, and as Bobby has said it depends on the type of trader, if it was the cowboy Arthur Daley types, then it can be very hard work indeed, and some don’t care about consumer law, they apparently just laugh in your face.
Other responsible dealers will try and fix the car, if a fault occurs, which is what the law requires them to do, if after this car has not been fixed to your satisfaction, then some will give a refund, and some will put up a fight.
A mix bag really, but the threads I have read, it’s a right pain in the backside, but unfortunately if needs to be done, then it needs to be done, regardless, good luck if you are in this sorry situation.
Could you give us the story, maybe you could get some solid advice on how to proceed.