Doesnt really matter. As I understand the rules of the game, in the first 6 months after purchase the seller has to prove that any problem was not there at the time of purchase. So you can reject the car or demand repair.
But dont wate valuable time with trading standards. They are a wet weekend.
No, you only have the right to reject for 30 days, after that you have to give the Dealer the chance to fix it. If the fix fails, you then have the right to reject.
Advice provided free of charge from a wet weekend of a trading standards enforcement chap, who has spent the last two weeks in court dealing with a multi million pound scam, hence not actually getting that excited about a one off fault with a car dealer that has yet to renege on his responsibilities.