Alistair Darling was at the centre of a new storm over the loss of personal data last night as The Times learnt that six more CDs containing confidential information were missing in the Revenue & Customs internal post.

The Revenue’s head office, which adjoins the Treasury, reported that the data was missing more than three weeks ago.

It follows the Chancellor’s announcement this week that the details of 25 million people on two CDs were lost in the post because a junior official failed to follow security procedures. The new loss, however, will strengthen Tory claims that the fiasco is a result of systemic failure.

Last night a spokesman for the Revenue said that the six missing discs held conversations between a tax credit claimant and one of its helplines. The discs were forwarded to a tax credits office in Preston by the claimant’s MP.

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Revenue officials asked for the discs to be sent to its main Whitehall address early last month. They were despatched on October 10 by internal mail, using TNT couriers — the same delivery system at the centre of the investigation into the missing child benefit data.

By October 30 they were reported missing, according to a Revenue spokesman, who said that a search was under way this weekend. “We take this loss extremely seriously and we are doing everything that we can to locate these CDs.”

The spokesman said that he was unable to say whether the CDs were password-protected or encrypted or had been sent by registered delivery.

Although the missing CDs contain confidential information about a single individual, the latest blunder will deepen the the Government’s embarrassment. MPs will want to know why Mr Darling did not tell the Commons in his statement that there was a second report of missing data.

A spokesman for the Treasury said that the Chancellor had not known of the six missing CDs when he made his statement on Tuesday. He also said that the latest loss was a “an operational matter for Revenue & Customs”.

The Times was informed about the latest loss after Revenue staff had a meeting with senior officials. They were asked to join the search for the confidential data — presumably so that they could be found before news of their loss leaked.

George Osborne, the Shadow Chancellor, demanded that Mr Darling return to the Commons to make a fresh statement setting out what he knew and when. “Alistair Darling’s version of events unravels day by day. The Chancellor needs to come before Parliament on Monday and explain himself,” he said.

The Conservatives also demanded the immediate suspension of a new government electronic database that holds the personal details of every child in England.

The £224 million ContactPoint register, which is due to be launched in April, lists the names, addresses, schools, GPs and, where applicable, social worker of the children. Where parents or children give consent, it could also include more sensitive information about whether children have used sexual or mental health services or had treatment for substance abuse.

Tim Loughton, Shadow Children’s Minister, has written to Beverly Hughes, the Children’s Minister, asking her to put the whole project on ice, amid fears about the security of the information. “After the Revenue & Customs fiasco this week, there are question marks over whether the security around ContactPoint is watertight,” he said.

The Government revealed last night that Ed Balls, the Schools and Children’s Secretary, ordered an urgent security review of ContactPoint on Tuesday.

ContactPoint will be password-protected, but the password will be available to around 330,000 vetted users.

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