Under the Sale of Goods Act and Sale and Supply of Goods to Consumer Regulations
If a car is defective, unsafe or otherwise doesn't conform to its description, the Sale of Goods Act and the Sale and Supply of Goods to Consumers Regulations (SOGA/SSGCR) give you rights across Europe to a refund, particularly if the fault occurs soon after buying, but also if there are problems a bit later on and there are unreasonable delays in getting the vehicle repaired or replaced. It's still best to complain about problems as soon as possible.
Repair and replacement
When you buy a defective car, repairs must not cause you significant inconvenience and the seller must bear all the costs. You can require the seller to reduce the purchase price if repairs or other remedies are unrealistic in a reasonable period of time.
Note that if you buy through an auction that you have – or could have – attended in person, your rights to refunds, repairs and replacements are more limited. These limitations don't apply to internet and telephone auctions.
Warranties and guarantees
After any warranty or guarantee period, or after six months, you might have to prove that any defect existed before you purchased. Guarantees are transferable to subsequent buyers.