A two-year police investigation that unearthed a £1bn used car fraud in the UK has forced Japanese carmakers to tighten controls within their franchised dealer networks.

The fraud, highlighted on BBC1's Watchdog programme, found that between 60,000 to 100,000 three and four-year-old vehicles have been stolen in Japan and sold on as new in the UK.

Mitsubishi Motors UK conceded that its UK franchised dealers would have serviced stolen imports and promised a clampdown.

A spokesman said: “Around 10% of servicing by our dealers is on grey imports and while that is a small amount, it's bound to have included stolen vehicles.”

He said dealers would now check VIN numbers and work with the police and DVLA to trace the stolen vehicles.