Doctor Sandy Macara, chairman of the British Medical Association's council, said that unless urgent action was taken to "de-identify" patient details "there is no doubt that down the line, government agencies will have access to information they should not."
The data would also be invaluable to banks, mortgage and insurance companies, employers as well as the Inland Revenue, security and immigration agencies, according to Dr Fleur Fisher, head of the Ethics Committee. She said the health service was poised to go down the same "slippery slope" as the United States, where there have been major breaches of confidentiality.
"It will blow the confidential relationship, between doctor and patient," Dr Fisher told the third day of the BMA's annual meeting in Brighton yesterday.
In one case in the US, a bank manager who was also a board member of a Health Maintenance Organisation (equivalent of a health authority or large health centre), obtained details of the medical history of some of his clients at the bank from the HMO's database. He then foreclosed on loans those who had been treated for cancer.
In another case, a woman who was standing for election to the Senate was devastated after someone leaked details from her medical records of a suicide attempt. "This woman had not even told her family," Dr Fisher said. "She was in fact elected and is now suing the hospital for $10m."
The BMA council is advising doctors, hospital trusts, and health authorities, to "just say no" to linking up to the network until confidentiality can be guaranteed via security measures such as encryption. These are now being reviewed by the Department of Health which has, until recently, proved resistant to the BMA's concerns.
Representatives of the 110,000-strong BMA membership endorsed the council's advice by a large majority, and now the association intends to mount a campaign to make patients aware of the risks and persuade health ministers to act.
At present, thousands of individual computers in the health service hold the medical records of millions of people. But an NHS-wide network - still at an embryonic stage - will be essential to the working of the internal market for billing and other administrative purposes.
Computer-held medical records - with names and addresses removed, which the Government says is sufficient to "de-identify" them - have already been sent to data processing companies by some hospitals. However, dates of birth and postcodes have been retained and this means the information can be traced back, Dr Fisher said. "The good news is that there are mechanisms [to protect confidentiality] and they are not overwhelmingly expensive. What we lack is the political will to do this."
The Government's announcement earlier this week of legislation to deny benefits to asylum seekers was condemned by doctors at the meeting yesterday. Dr Evan Harris, who treats detainees at Campsfield House, near Oxford, said: "This legislation is so tawdry and the motive so dishonourable that no civilised society would pass it into law." It will be introduced during the Third Reading of the Asylum and Immigration Bill in the Lords on Monday.Reuse content