The decision to blame a junior official for the loss of 25 million child benefit records was unravelling after e-mails showed senior managers were consulted on how the data should be sent.

E-mails between Revenue & Customs officials also show that officials were worried about the cost of removing personal details before data were sent to the National Audit Office.

On October 2, two weeks before the discs were sent, the NAO told HMRC to ensure the CDs were sent “as safely as possible due to their content”.

Alistair Darling, the Chancellor, was accused of a cover-up last night after it emerged that more senior officials were aware of the procedure. The Treasury insisted that it had never suggested that one person was to blame.

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The exchange, released by the NAO, includes an e-mail stating: “I do not need address, bank or parent details in download — are these removable to make the file smaller?” HMRC replies: “I must stress we must make use of data we hold and not overburden the business by asking them to run additional data scans/filters that may incur a cost to the department.” The data would be transferred by CD-Rom. According to the NAO, this e-mail was sent by a junior manager but copied to the “HMRC Process Owner for Child Benefit”, Nigel Jordan, 49, a career civil servant. The exchange of e-mails, in March, related to an earlier request by the NAO for child benefit data, which appears to have set a precedent.

It was reported last night that it would have cost HMRC £5,000 to edit the data on the discs.

Yesterday the Conservatives said that evidence of senior officials being involved contradicted government statements. Mr Darling told the Commons on Tuesday: “It cannot be left to someone at a junior level to decide whether information should be downloaded — and then, in this case, posted in a way that was totally insecure.”

George Osborne, the Shadow Chancellor, said: “The Chancellor must explain the apparent inconsistencies.” The Treasury said: “Everything in the e-mails is consistent with the Chancellor’s statement. We cannot pre-empt the outcome of investigations.”

The HMRC wrote to all child benefit claimants that the missing data “is still likely to be on government property”. Police continued to search the child benefit office in Tyne and Wear.

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