'We have had all 20 cars go wrong,' said John Waldock, workshop supervisor with Hertfordshire police. 'It is an assembly problem at the Isuzu factory in Japan leading to oil leaks from the end cover gasket. It is a serious problem and oil can get on to the brakes. For police use that is bad. The problem is resolved under the warranty scheme with the cars being returned to the local Lex dealership.

A Vauxhall spokesman said gearbox leaks had been a problem but were solved by May. He said there was no recall because it was not a safety issue but retailers had been told to check cars as they came in for routine visits. Fleet operators should tell drivers to keep an eye on their drives for tell-tale red stains.