Used car values have this month suffered their worst slump since the current market downturn started in July 1998, falling by 7.7% compared to May last year.

Cap Black Book senior editor Daren Wiseman blamed adverse publicity surrounding new car prices and confusion over the Competition Commission inquiry recommendations for the collapse.

“Customers are going to dealers and saying they are waiting for new car prices to fall because that means used prices will too,” he said.

This week Mr Wiseman predicted values would continue to fall until action was taken to settle the new car market.