Chancellor Alistair Darling must return to Parliament to clear up discrepancies in his statement on the loss of child benefit data, Tories have demanded.
Mr Darling told MPs on Tuesday a junior HM Revenue and Customs employee was to blame for two computer discs containing 25m claimants' details going missing.
But shadow chancellor George Osborne said documents suggested senior officials were aware of what happened.
Meanwhile, police are searching a courier firm's depots for the discs.
See sequence of events in the lost CDs scandal
And on Saturday, HM Revenue and Customs (HMRC) confirmed that a further six data discs had gone missing in transit between its offices in Preston and London.
The discs, which were reported missing on 30 October, contained recorded conversations between a member of staff and a customer making a complaint.
Credit monitoring
The first two missing discs hold the personal details of all families in the UK with a child under 16.
The data on them includes the name, address, date of birth, National Insurance number and, where relevant, bank details of 25 million people.
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The discs were intended for the National Audit Office (NAO) in London, but never arrived from HMRC's office in Washington, Tyne and Wear.
Writing in the Sunday Telegraph, Mr Osborne called on the chancellor to come before the House of Commons to explain "what really happened" in the light of documents released by auditors.
He added: "In a crisis like this, the chancellor owes it to worried families to tell them the whole truth."
Mr Osborne has also urged the government to offer free credit monitoring to those affected.
'No proof'
A core team of 47 detectives from the Specialist and Economic Crime Directorate has been involved in the search for the original two discs.
Police are now focusing on depots of the courier company TNT after completing inquiries at HMRC's offices.
A spokesman for TNT confirmed its premises in London had been searched on Friday night and said the company was fully co-operating with police.
But he added that it was impossible to say whether the CDs had entered TNT's system.
"All the evidence points to the fact that these discs are still on our premises"
"HMRC confirmed to us last night that they use two other companies for internal mail."
An HMRC spokesman confirmed the agency did use other courier services and said that the hunt for the discs would be "wide-ranging and comprehensive".
"All the evidence points to the fact that these discs are still on our premises," he added.
People affected by the loss of the child benefit discs are being asked to check their bank accounts for any "irregular activity", but have been told there is no need to close accounts as the details would not be sufficient to allow fraudsters to access them.
However, they are advised not to give out personal or account details "requested unexpectedly" by phone or e-mail.
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