As many as nine million employment files held by HM Revenue & Customs could be wrong, according to an internal review.

With around 45 million record held, one in five may contain mistakes, raising fears that people won't be paying the correct amount of tax this year.

It's another big problem for the tax office which has just started sending out letters to tens of thousands of workers telling them they've been on the wrong tax code since 2008.

Almost 1.5m Britons face having to cough up around £1,500 to cover a shortfall in tax paid.

HMRC has been worrying about the accuracy of its records since January when it installed a new £400m computer system. The machine may have generated the wrong tax codes for 2010-11.

That convinced HMRC to review all its employment records, which has found 9.3m of them "potentially at risk of error".

Taxpayers have been urged to check their codes and tax bills, although HMRC insists all the problems have been rectified.

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