Paul Gray, the chairman of Revenue and Customs, has resigned over "a substantial operational failure" in the department.

His resignation comes amidst fears that HMRC may have lost a disc containing the personal records, including bank details, of up to 15 million child benefit claimants.

Gray admitted in his resignation letter that HMRC still faced "some major issues where we need to do better" but made no explicit reference to HMRC's recent failures in protecting personal data.

Earlier this month HMRC admitted that it had lost a CD containing 15,000 names, national insurance numbers and dates of birth of thousands of holders of Standard Life pensions. The data was “lost in transit by HMRC’s external courier”, the agency said.

Chancellor Alistair Darling will make a House of Commons statement on the crisis at 15.30 GMT today (20 November).