Simply reject the car as "not of satisfactory quality" as is your right under The Consumer Rights Act 2015 and preceding Acts and Case Law and demand your money back. If the dealer refuses to take it back, demand a substitute car until your new car is fixed. If he refuses to do that as well, see a solicitor and take immediate legal action. If the dealer choses the second option, fully detail your complaint in writing, send it to the dealer principal by Post Office Special Delivery, keep a copy and staple the certificate of posting to the copy so it becomes a matter of record for the courts.