Mr Leigh chairs the cross-party public accounts committee

The influential Commons Accounts Committee has urged the Inland Revenue to increase current prosecution levels.

Tory Edward Leigh, the committee chairman, said investigations and prosecutions were low compared to the "potential loss to the public purse".

He said: "I urge the Revenue to step up considerably fraud investigation."

Publicise fraud?

"Indeed, with only 400 serious fraud investigations a year against 30 million customers, those contemplating tax fraud may well calculate that the chance of being caught is remote.

"I urge the Revenue to step up considerably their fraud investigation work and to pilot national publicity campaigns highlighting the unacceptability of fraud and the consequence of getting caught, along the lines of those undertaken by the Department for Work and Pensions and HM Customs and Excise."

In their report on tackling fraud, the cross-party committee said the Revenue had not calculated the tax gap - the difference between what tax take ought to be and the amount actually collected.

�214bn collected

The MPs called for the Inland Revenue to publish a strategy for the prevention and detection of fraud and for deterring it.

The committee said that the Inland Revenue collected around half of all the public revenue - �214bn in direct taxes and national insurance in 2001/2 from about 30 million taxpayers.

It also distributes around �5.7bn in tax credits to more than a million low-income claimants - a figure set to rise above �15bn in 2003/4.

According to the committee, the Department for Work and Pensions prosecutes more than 20 times as many cases per �100m spent.