LONDON — Personal information about patients in Britain's free health-care system has been lost, the Department of Health acknowledged Sunday — the third loss of data about the public by a government service this year.

Nine of the trusts that oversee Britain's National Health Service have acknowledged losing information about patients, an apparent violation of strict data protection rules by the health service.

The Department of Health said that it did not have an overall number on the patients whose personal data have been lost. But it said they have been informed and that there is no evidence that the information has fallen "into the wrong hands."

"Investigations are under way in all the trusts involved and action will be taken against anyone who has failed to fulfill their legal responsibilities," the government agency said in a statement.

The Sunday Mirror newspaper reported that hundreds of thousands of adults and children are thought to have been affected by the breaches, which emerged as part of a government-wide data security review.

The NHS trusts are essentially public sector corporations that oversee state-provided free health care in England and Wales.

One of the NHS trusts involved, City and Hackney Primary Care Trust, reportedly lost the details of 160,000 children after a computer disk failed to arrive at its destination at St. Leonard's Hospital in east London.

The loss at the Gloucester Partnership Foundation Trust, in southwest England, consisted of archive records relating to patients treated 40 years ago — none of them still alive.

Details about the number of patients affected at the other seven trusts were not immediately available on Sunday.

Earlier this month, Britain's government said that a computer disk drive containing personal information on 3 million driving test candidates had been lost in the United States.

That report followed the loss by tax officials of sensitive data — including banking records — on nearly half of Britain's population.

Two computer disks from a tax and welfare department containing names, addresses, national insurance numbers and, in some cases, banking details for 25 million adults and children disappeared while being sent by internal mail, ministers said in November.

A series of reviews launched because of the errors found that other government departments also had concerns about data handling.