You have the right to reject a faulty car within 30 days and then up to six months if you have given the dealer one attempt to fix a fault. After six months you have to prove the fault was present when you bought the car which will probably be very difficult if you bought it one year ago even if still under warranty. You will need solid proof that the car was faulty the day you bought it rather than the fault or faults occurring the day afterwards.
https://www.thecarexpert.co.uk/rejecting-a-car/