The Office of Fair Trading and the Society of Motor Manufacturers and Traders yesterday launched a code of practice to help new car buyers.

The code sets out minimum standards of service that car buyers can expect from manufacturers if the car fails within the warranty. It also sets out fines for manufacturers who consistently fail consumers.

The consumer group Which? said the code was "feeble, vague and ineffectual". It said round 2.4m cars were bought in the UK over the past 12 months and the OFT received nearly 20,000 complaints last year about new cars, making it the top "headache" industry.

The consumer group said the maximum fine was just £5,000 - the equivalent of 25p per car sold in a month by the biggest makers.

The SMMT said the code established clearly that car manufacturers must honour warranties, even if the car has been serviced outside its dealer network. And in future, buyers will know from SMMT reports which manufacturers attract the most complaints.