The government's change of policy on patient records, disclosed in the Guardian today, is the first departure from a roadmap drawn by Tony Blair in 2002 when he approved a scheme to spend billions on a new IT system for the NHS.

The prime minister was captivated by the vision of a national database containing the medical records of 50 million patients throughout England. Heads of the corporations developing cutting edge technology convinced him that lives could be saved if doctors, nurses and paramedics could gain instant access to key information about patients that might cause conventional treatments to cause life-threatening reactions.

Instead of consultants waiting for hours to locate the patient's GP and ask for relevant information, a paramedic on the scene would be able to access data from a palmtop computer. Who could object?

Mr Blair thought nobody would when he authorised what eventually became a £12bn scheme to connect more than 30,000 GPs to nearly 300 hospitals and their outposts in the ambulance service.

The NHS's national programme for IT - the biggest non-military computer procurement in the world - had several objectives, including the creation of an electronic booking system for patient appointments and an electronic storage system for x-rays and scans that brought a huge leap forward in opportunities for accurate diagnosis. From the outset, the patient record was a key component, but nobody thought to ask whether patients minded having medical details put on a national system which could potentially be accessed by a large proportion of the NHS's 1.3 million staff.

The British Medical Association was divided. Consultants in hospitals with poor IT systems were enthusiastic. GPs whose IT systems tended to be more up to date were anxious about sharing patients' medical secrets without asking consent.

Lord Warner, the health minister, set up a taskforce under Harry Cayton, the patients' "tsar", to work out a compromise between GPs who wanted patients to choose to opt into the scheme and others who feared the most vulnerable patients would not bother to make the choice.

For civil liberties campaigners, the internal debate missed the point. They mistrusted promises of electronic security locks. On November 1, the Guardian carried a coupon compiled by Ross Anderson, professor of security engineering at Cambridge University. It prompted 1,351 people to write to Patricia Hewitt, the health secretary, using the coupon or words from it, to demand their medical records should not be uploaded.

According to Mr Cayton, this intervention changed the terms of debate as the taskforce began to discuss the possibility of an opt-out from the upload.

There was no hint of this when the Department of Health wrote robustly to the 1,351 objectors, refusing to comply with their wishes. But Mr Cayton's report on Monday will signal a change of heart.

Lord Warner's response will fall well short of a guarantee of a complete opt-out from the system. But he said the government is now concentrating on how to give the opt-out, not whether to give it.

Facts on file

What are they planning to do with medical records?

The government wants GPs to put a summary of every patient's medical notes on a national computer database. Ministers think lives could be saved if doctors could get hold of key information in an emergency.

Is that a problem?

Civil liberty campaigners think people's medical secrets will be vulnerable to computer hackers. Ministers promise state-of-the-art security to prevent unauthorised access.

Have ministers made a U-turn?

They said nobody could stop their records being uploaded. On Monday they will say the question is how to let people opt out, not whether.

When will patients get to choose?

In two trial areas, uploading starts in the spring. The rest of the UK will follow later next year.