Foreign drivers have fuelled an alarming rise in the number of road tax dodgers, a report by MPs reveals.
Britain now has One in 20 vehicles untaxed, costing law-abiding citizens at least £214million last year.
Yet the Government and the Driver Vehicle Licensing Agency admit they have no idea how big the problem is, says a highly critical report by Parliamentary watchdogs.
They also warn that road tax system could easily become "a complete laughing stock".
Evasion of Vehicle Excise Duty rose to 5 per cent in 2006, up from 3.6 per cent in 2005.
Among motorcyclists, the evasion rate increased from 30 per cent to 38 per cent.
Road tax from 35million cars raises about £5billion a year, although only a fraction of this goes into transport.
Yet many foreign drivers, increasingly from Eastern Europe, do not bother to register their cars as they must by law after six months.
And if they commit motoring crimes they cannot be traced and will rarely be pursued by police or the authorities.
Persistent evaders avoid paying tax, parking tickets, speeding fines and congestion charges. Some copy or "clone" number plates from vehicles of law-abiding drivers.
The problem has become so severe that ministers have abandoned targets for tackling the dodgers.
Committee chairman Edward Leigh said: "Motorists and motorcyclists who refuse to pay road tax are stealing from law-abiding taxpayers and unlicensed cars are often associated with other forms of crime.
"And yet the Department for Transport (DoT) and the DVLA are losing ground in their fight against VED evasion."