Hundreds of thousands of people were thought to have been affected by the breaches of strict data protection rules by the health service.

But the Department of Health said it thought the lost data fiasco involved a total of 168,000 patients.

Critics said the disclosure raised fresh questions about the Government's handling of confidential personal data and the future of a new centralised information technology system for the NHS.

It follows anger at the loss of child benefit claimants' details by HM Revenue and Customs and those of three million learner drivers by a Driver and Vehicle Licensing Agency contractor.

Police are still hunting two customs computer discs which went missing. Transport Secretary Ruth Kelly revealed motorists' details were lost in Iowa.

Richard Vautrey, deputy chairman of the British Medical
Association's GPs' committee, said: "Patients need to be absolutely confident that the information that is held securely cannot be lost in some haphazard way as appears to be the case today."

He said the development was especially worrying given the Government's plans for a centralised NHS computer network, Connecting for Health, featuring every patient's records.

Joyce Robins, of patient support group Patient Care, said: "Given the carelessness and lack of accountability in the NHS, this could be the end of patient confidentiality."

Trusts involved were: Bolton Royal Hospital; City and Hackney Primary Care Trust; Maidstone and Tunbridge Wells; Sutton and Merton PCT, Sefton Merseyside PCT; Mid-Essex Care Trust; East and North Hertfordshire, Norfolk and Norwich and Gloucester Partnership Foundation Trust.

A spokesperson for the Department of Health said: "The suggestion that the NHS has misplaced hundreds of thousands of patient records is completely misleading.

"One incident involved the clinical details of 160,000 patients, but this data is encrypted to an extremely high level of security.

"We believe that an additional 8,000 patients in total may have been affected, but even amongst these only a small proportion involves some clinical data, and there is no evidence that this has fallen into the wrong hands."

The spokesperson said the episode would not prevent the central computer database going ahead.