Flawed legislation being proposed by the Tory-Lib Dem coalition could remove patient confidentiality, according to a doctors' group.
Some clauses of the Health and Social Care Bill that relate to information sharing throw up "serious concerns" for the British Medical Association.
The proposals do not guarantee patients that their identities will be kept secret because broad powers are be handed over to several bodies, such as health ministers, the NHS Information Centre and the Commissioning Board, which will all be able to obtain and publicise people's personal information, it said.
The BMA wrote to health minister Simon Burns to outline its criticisms.
The doctors' group believes the legislation, if passed, would force patients to withhold important information because they would not trust it would be kept confidential. The letter points out that the Bill allows the bodies "to obtain and disclose confidential patient information for any number of unspecified health purposes".
It reads: "As currently drafted, there is very little in the Bill relating to confidentiality and information governance controls, which are so fundamental to medical practice and the trust-based relationship between doctors and patients."
A Department of Health spokesman said : "There is no question of the Health and Social Care Bill undermining the confidentiality of patients and their clinicians. The Bill does not change any of the existing legal safeguards, which are set out in the Data Protection Act and the common law of confidence."