What if those records lost by HM Revenue & Customs (HMRC) are not tucked down the back of Alistair Darling’s sofa but are in the hands of serious cybercriminals?

How much danger is the British public really in?

The data lost by HMRC includes the names, addresses, children’s names, dates of birth, national insurance numbers, bank details (account numbers and branch addresses) for more than seven million families, about 25 million individuals.

By itself, that information is not enough to, say, access a bank account and withdraw money – it does not provide what cybercriminals call “the full deck”.

Customers with online accounts, for instance, also have passwords.

Moreover, it does not allow for the present con of choice, which exploits “customer not present” transactions, where fraudsters make a copy of a credit or debit card and then use it in a shop (usually overseas) that doesn’t have a chip-and-pin system in place and does not ask for the three-digit security number on the back of most cards.

Similarly, walking into a high street bank and opening an account has been made much harder in recent years by anti-money-laundering laws.

HSBC, for example, requires new customers to present a full passport or national ID card in person at one of its branches – or a tax letter from HMRC.

To verify your address the bank would require a bank, building society or credit union statement or passbook or a utility bill.

But serious would-be fraudsters have access to these type of resources, tools that help to complete that “full deck”, according to Graham Cluley, of Sophos, the technology security group.

He said: "Identity thieves often work closely with credit card cloners and forgers of other ID material.”

That makes the HMRC information extremely valuable.

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