More than 2m untaxed and uninsured drivers are laughing at the law as prosecution rates more than halve in eight years

More than two million rogue drivers escaped prosecution last year as an underclass of untaxed and uninsured drivers grows at an alarming rate, figures reveal today.

They show that there are 63 per cent more road tax evaders than eight years ago - yet only half the number of successful prosecutions.

Today, a driver who does not pay road tax has a one in 20 chance of being prosecuted against a one in six chance in 1999.

The figures were unearthed by Tory transport spokesman Theresa Villiers from answers to a series of parliamentary questions.

Miss Villiers said: 'These figures are a shocking indictment of the Government's truly hopeless record on dealing with rogue drivers.

'The Government needs to get a grip on this issue. What these stats highlight is that, under this Government, things have been getting steadily worse.

'Rogue drivers without tax or insurance are a menace to other road users.

The direct result of Labour's incompetence in dealing with rogue drivers is that our roads are more dangerous.'

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The Department for Transport figures show the estimated number of untaxed vehicles on the roads has soared from 1.33million in 1999 to 2.17million in 2006, an increase of 63 per cent.

Yet over the same period, the number of successful prosecutions for car tax offences has almost halved from 204,606 to 103,108.

Ministers estimate the lost revenue is £79million for 2007-2008 alone.

In January, a report by the Commons public accounts committee said the Government's record on road tax was 'poor' and it was 'losing ground' against the evaders.

The system risked becoming 'a complete laughing stock' and spiralling out of control.

A flood of foreign motorists driving illegally, many from eastern Europe, has been blamed by MPs for contributing to the number of cars that are untaxed or unlicensed - where the documents required to get a tax disc are not in order.

Edward Leigh MP, chairman of the public accounts committee, said: 'Motorists and motorcyclists who refuse to pay road tax are stealing from law-abiding taxpayers. Unlicensed cars are often associated with other forms of crime.'

Sheila Rainger, of the RAC Foundation, said the figures were a ' wakeup call for better enforcement'.

She added: 'Motorists driving without tax are also more likely to be driving uninsured and without an MoT.

Responsible motorists are not only picking up the tab for evaders, they are also being put at risk by them. The Government needs to boost the number of traffic police carrying out on-road crackdowns, so that the motoring underclass and the hardcore tax dodgers are the ones feeling the pressure, not the law-abiding motorist.'

Paul Watters, of the AA, said: 'We fear that today's road tax evasions figures are actually the tip of the iceberg. In January, the public accounts committee reported that losses to the Treasury in 2006 were £214million, more than double that quoted today.'

A Department for Transport spokesman said: 'The DVLA and the department, together with the police and local authorities, are determined to force tax evaders off the roads. We are targeting persistent evaders and seizing 100,000 unlicensed vehicles each year.

'From September, new legislation will allow police, DVLA and local authorities to take action against unlicensed vehicles even if they are not parked on public roads.'

Under the law, motorists will receive an £80 penalty charge notice through the post if they fail to tax their cars on time, with a theoretical maximum fine for non-payment of £1,000.

But critics say the sanction is toothless against persistent offenders, who are also likely to be uninsured, without a valid driving licence, or MoT. This 'underclass' does not show up on the DVLA computer as having a valid address.