How to go down the legal route
You must prove that you’ve tried all reasonable means to resolve the dispute before considering an approach to the courts. If you bought a car from a trader, communicate as much as possible and give adequate opportunities for the issues to be rectified. Your local Citizens Advice Centre will be able to provide general guidance about statutory rights in relation to your dispute.
Your next stage may be to take independent legal advice. You can also pursue a claim via the small claims track (for claims up to £10,000 in value) of your County Court; doing so is a far more straightforward and inexpensive process than many people imagine. Regardless of how you wish to resolve the dispute, be reasonable and clear about where you want to be at the end of it.