We now have the technology to abolish privacy altogether. A competent policeman could solve almost any crime if given a complete record of all the data collected by our phones, the computers that we use at desks all day, and, soon, the innumerable household devices that monitor and report to central servers their and their users’ operation, the coming wave of health monitoring devices and even Britain’s unparalleled network of CCTV monitors. The data would show where we had been, how we had got there, who we had met, what we had asked search engines, who we had talked to – and whether we had taken any measures to hide any of this. All that would be available without tapping a single phone call.

To some people, and the home secretary may be one of them, this looks like an ideal state. But the concentration of such power would inevitably lead to its abuse – and in new and horrible ways. If information is power, complete information will tend to corrupt completely. The state that held all that knowledge in its hands would turn into a tyranny. Almost as dangerously, much of it would leak out to criminals.

What keeps this nightmare at bay is two things. The first, and most important, is that the information is not all held centrally. In fact much of it, like the content of emails that Google scans in order to display ads alongside them, is never read by human eyes at all. The second restraining factor is the law and that is less of a protection just when we need it to be more of one. The present laws governing government surveillance are – everyone agrees – a tattered and outdated patchwork. The problem is that Theresa May’s proposed replacement puts in place of the old patchwork something much more like a fishnet – wonderfully flexible but made up mostly of holes.

All three parliamentary committees that have examined her proposals have criticised them. The powers she demands are uncosted, unjustified and very probably unworkable. Two aspects are particularly conspicuous and vulnerable to criticism. The first is the demand that phone companies and internet service providers keep records of all connections made through them going back for a year. If it were to be effective, it would have to cover all public Wi-Fi networks, including those in cafes and libraries. This represents such a huge amount of data that no one knows whether it would even be technically feasible to collect. What is certain is that even the attempt would cost many times what the Home Office presently forecasts – the official estimate is around £150m. If this is like any other government computing project, it would easily end up costing 10 times as much before it is abandoned as not working.

The second warning flag is Mrs May’s insistence that the new powers would be “technologically neutral”. That’s impossible. The interplay between technology and privacy is one of constant change. Privacy is a legal and social construct while technology develops to its own quite independent laws. Without a clear and concise statement of the principles on which the law is supposed to operate, her draft bill is no more than 300 pages of misleading detail. It needs to be rewritten. It needs realistic costing. And it will need to be revisited in five years’ time when there will be fresh threats and challenges from ubiquitous technology.