At least 30% of self assessment tax returns contain errors, according to a report published today by an influential House of Commons committee.

The public accounts committee report will say that the calculation errors could be costing the state as much as £2.8bn in lost tax revenues.

Edward Leigh, chairman of the PAC, said: 'Taxpayers are increasingly going to the wire when it comes to filing their tax returns, despite HM Revenue & Customs’ advertising campaigns. The department then has to process a lot of returns in a short time, leading to more official errors. Different filing dates for different groups of taxpayers would spread the load.

'Taxpayers themselves make errors in about a third of tax returns, costing an enormous £2.8bn in lost tax. HMRC needs to provide clear information on how to avoid the most common mistakes. It should improve the training of its call centre staff and the access to specialist advice.'

About £16bn a year is collected from self-assessment, with forms going out to an estimated 10 million people. HMRC reached its target of having 90.6% of forms returned by the 31 January deadline, but will have to reach 93% by January 2008.