British Prime Minister Gordon Brown's government suffered new embarrassment over missing data on Monday when it revealed one of its contractors had lost the details of 3 million learner drivers.

The revelation came weeks after the government admitted it had lost computer discs containing the names and bank account details of 25 million people, exposing nearly half the population to possible fraud and identity theft.

The opposition Conservatives accused the government of incompetence over the data loss, the latest in a series of mishaps that have caused the popularity of Brown's six-month-old government to plunge.

Transport Secretary Ruth Kelly told parliament a private contractor reported in May that a hard disc drive had gone missing from a facility in Iowa in the U.S.

It contained the names, addresses and other details of more than three million candidates for a theory test taken by learner drivers in Britain. The disc drive did not contain any bank account or credit card details, Kelly said.

"I apologize for any uncertainty or concern that these individuals may experience," she said.

She also revealed that two discs containing the details of 7,500 vehicles and the names and addresses of their owners had been lost in transit.

She announced steps to tighten up the security of personal data held by government agencies.

Conservative transport spokeswoman Theresa Villiers said the loss was "further evidence of systemic failure in the government's handling of private data, evidence of a basic lack of competence by this government."

"Quite simply the government is failing in its duty to obey its own laws on data protection," she said.

An opinion poll on Sunday showed Brown's Labor Party trailing the Conservatives by the largest margin in more than 15 years.

A YouGov poll for the Sunday Times put Labor on 32 percent, 13 points behind the Conservatives. Brown's personal rating has also slumped since he took over from Tony Blair in June.

Finance minister Alistair Darling told parliament earlier there was no sign that the discs containing the details of 25 million people had fallen into criminal hands.