The Treasury is losing £200 million through non-payment of road tax, parliament's spending watchdog has warned.

Data released on Friday reveals that nearly five per cent of total revenue is being lost through evasion.

The worst offenders are motorcycle users - 22.9 per cent of whom are failing to pay.

The report called on the Driver and Vehicle Licensing Agency (DVLA) - which collected £4.6 billion of vehicle excise duty in 2002/03 - to step up efforts to tackle non-payment.

Across the country as a whole evasion levels have risen to 4.5 per cent - up from 3.9 per cent in 1999.

Evasion levels have risen in seven of 11 regions in Great Britain, with the greatest increases occurring in the East of England and Greater London.

The DVLA already uses a variety of anti-evasion measures - including wheel clamping and automatic number-plate reading equipment.

These generated £69 million through fines over the last year.

NAO chief Sir John Bourne said: "It is clear that the DVLA continues to recognise the importance of tackling the evasion of vehicle excise duty.

"But evasion levels are rising and there remains considerable scope for anti-evasion measures to be extended and deployed in a more coherent manner.

He added that the DVLA should extend the use of automatic number-plate readers and work with local authorities and police forces to target evasion.