A few days ago, I dropped into my GP's surgery to pick up a prescription and was confronted by one of those large, floor-mounted pop-up displays that one finds in exhibitions, trade fairs and circuses. It informed me of an exciting new scheme by which the "quality of care and health services" would be "improved" by "sharing" information about the care I receive with those who plan health and social care services, as well as with "approved researchers and organisations outside the NHS".

The mechanism by which this "sharing" was to be accomplished, namely uploading one's confidential medical records to a huge database, was nowhere mentioned in the poster. Indeed, the word "database" appears nowhere either in the poster or in the official leaflet that is being junk-mailed to every household in the land. Instead, there is a lot of soothing verbiage extolling the benefits of uploading all our medical records to a giant server farm. Doing so will, for example, enable the NHS to "find more effective ways of preventing, treating and managing illnesses", "guide decisions about how to manage NHS resources so that they can best support the treatment and care of all patients", etc.

There are also the statutory assurances for those wimps and technophobes opposed to the march of progress. "Records are linked in a secure system so your identity is protected," the leaflet burbles. "Details that could identify you will be removed before your information is made available to others, such as those planning NHS services and approved researchers." Finally, right at the end, we get to the heart of the matter. "Do I need to do anything?" asks the leaflet. Answer: "If you are happy for your information to be shared you do not need to do anything. There is no form to fill in and nothing to sign. And you can change your mind at any time." If you're unhappy, you have to tell your GP.

It's the old standby of the computer industry, the default option, now sanctified by an outfit in Whitehall called the "Nudge Unit" dedicated to inflicting the doctrine of Messrs Thaler and Sunstein on the citizenry. This doctrine says that if you want people to do something then you make it the option that requires no action by them. Inertia rules OK, in other words, human nature being what it is.

Those planning this healthcare data-grab are clearly hoping that citizen inertia will enable them to achieve their aim, which is to make our most intimate personal details available for data-mining by "approved researchers". If they succeed, then, starting in March, the medical data of everyone who has not opted out will be uploaded to the repository controlled by the NHS information centre. And for the first time the medical history of the entire nation will have been stored in one place.

What's wrong with this? How long have you got? In the first place, there is the fact that the category of "approved researchers" doesn't just include university researchers, doctors and NHS planners. The data will also be sold to corporate researchers working for insurance, pharmaceutical and other firms.

Then there is the question of data security. If we have learned anything from the Bradley/Chelsea Manning affair, it is that large centralised databases to which many people have access are intrinsically insecure. One day, there will be a breach of this NHS repository, after which there will be the usual hand-wringing ministerial statement assuring us that the stable door is now well and truly shut.

Finally, and most important, there is the question of privacy. The data that will be sold to "approved researchers" will, we are told, be "scrubbed" of some personal identifiers – but not enough to make the information completely anonymous.

However, Mark Davies, the repository's "public assurance" director, told the Guardian that there was only a "small risk" certain patients could be "re-identified" because insurers, pharmaceutical groups and other health sector companies had their own medical data that could be matched against the "pseudonymised" records. "You may be able to identify people if you had a lot of data. It depends on how people will use the data once they have it. But I think it is a small, theoretical risk," he said.

All of which makes one wonder what Davies has been smoking. (If his scheme goes ahead, his life insurance company will soon know.) In the meantime, how about not letting inertia rule OK? Head over to medconfidential.org, download a form, fill it in and drop it in to your GP. And if you have kids, do one for each of them too, because when they grow up they may not thank you for compromising their privacy.