The Consumer Rights Act 2015 applies to all vehicle sales. This means that the vehicle must be of satisfactory quality, fit for purpose, and as described. 

If a major issue arises within the first 30 days—such as a serious fault or misrepresentation—you can return the car for a full refund. 

After 30 days, the seller has one chance to repair or replace the vehicle, with repair usually being the preferred option. If the issue persists or a new fault develops, you can either request a partial refund while keeping the car or reject it entirely for a refund, minus a deduction based on the miles driven.