New Government figures show road tax evasion is falling overall - yet increasing among motorcyclists.
The estimated amount of Vehicle Excise Duty (VED) not paid by motorcyclists in 2009 stands at around 3.2%, compared with 2.3% in 2008.
But the overall rate of untaxed vehicles on roads in Britain this year is estimated at 0.5%, which has decreased from last year's 0.7%.
VED evasion could cost around £49 million in lost revenue in 2008/09, compared with an estimated £79 million in 2007/08.
For all vehicles, the East Midlands had the lowest evasion rate this year at 0.4%, while Scotland had the highest at 0.7%.
Driver and Vehicle Licensing Agency chief executive Noel Shanahan said: "We've made it easier than ever to license a vehicle and our online road tax renewal system continues to be a great success.
"We are also cracking down on people who flout the law, so I am delighted that we have seen another fall in the level of road tax evasion.
"We know that the overwhelming majority of motorists comply with the law and properly license their vehicles, but we're committed to continue to take serious action against the very small minority who don't."
Motorists and motorcyclists who neglect to pay their road tax are also invalidating their insurance cover.
© Press Association 2009