“The difficulty is that their gearboxes may not have been machined to accept the correct sender device,” he explains.

Mechanical adapters are available and have been approved by the Vehicle and Operator Services Agency (VOSA), says Mair, but only for a limited number of light commercials. They include the front-wheel drive Ford Transit, he says, and Ford's Ranger pick-up. The use of electronic adapters is still under discussion.

In Mair's view no attempt should be made to tow a trailer heavy enough to make the Drivers' Hours rules an issue with a vehicle that should be fitted with a digital unit, but cannot take one, until the situation is resolved. While VOSA may be prepared to take a pragmatic approach and view things on a case-by-case basis, there is still the risk that the operator will be prosecuted.