SCORES of vans were stopped in a crackdown on criminal drivers by police, trading standards and customs and excise agents.
They stopped 49 vehicles in Ashridge and on the A41 near Cow Roast as part of Operation Scorpion.
Thirty-nine were dip-tested to see if they were using red diesel. The fuel - designed for farm equipment such as tractors - has less tax on it than normal diesel.
But it is illegal for normal road-users to cash in on the cheaper fuel, which is often stolen from farms.
One van was towed during the operation last Tuesday after its owner was unable to pay a £400 on-the-spot fine for using red diesel.
Police also stopped two known criminals from outside Herts and the crooks gave them intelligence to help stop future crimes.
Berkhamsted police sergeant Peter Huffer said: “We intend to carry on Operation Scorpion throughout summer and regular police activity will continue to disrupt crime in the area.”