Think of the capacity of a large football stadium. That is the number of people – 61,000 – who were stopped at entry points into Britain last year under the infamous schedule 7 of the 2001 Terrorism Act (the one used against Glenn Greenwald's partner, David Miranda). Amazingly, the total has actually gone down compared to a few years earlier. Ask yourself, are there really that many people transiting the UK who may pose a terrorist threat?

Governments, Tory and Labour, have long adopted the dragnet approach to criminal justice. Nobody is safe. Everyone is a potential terrorist. Therefore keep tabs on as many as possible, just in case now or sometime in the future they might get up to no good. Why enact a targeted law when you can have a vague one? Why restrain your security apparatus when you don't have to? By the time Tony Blair left office in 2007, he had built a surveillance state unrivalled anywhere in the democratic world. Parliament passed 45 criminal justice laws – more than the total for the previous century – creating more than 3,000 new criminal offences. That corresponded to two new offences for each day parliament sat during his premiership.

Some were technical updates; many might have been uncontroversial. But the ministerial hyperactivity points to a political mindset that was never satisfied with powers as they were. Gordon Brown's brief rule continued this trend, trying to extend the length of pre-trial custody. The coalition came to power in 2010 promising to reverse the excesses of the past; its Freedom Act did make some improvements, including killing off (for now) identity cards.

After that brief genuflection towards a more sensible balance between security and liberty, Theresa May's Home Office went back to business as usual. It successfully steered through secret courts and attempted to introduce the "snoopers' charter" – which, as the Prism leaks testify, is largely redundant, as they are doing it anyway. As they justify the inexorable extension of security powers, ministers of all hues resort to two mantras: "If you've done nothing wrong, you've got nothing to hide; and "If only you knew what we know …"

The rot set in with the 2000 Terrorism Act (note the timing, this was before 9/11). This was portrayed as a tidying-up exercise, but was anything but. The legislation deliberately broadened interpretations of terrorism, allowing the police to arrest people for "offences" including filming them, photographing public places or attempting to get to demonstrations (all favoured tactics during Soviet rule). Section 44 of the act was the mechanism by which anyone could be stopped and searched anywhere, just in case. No suspicion or justification was needed. This was the mainland equivalent of schedule 7. Eventually, section 44 was repealed, but other provisions in the act can still be applied for similar purposes. Tellingly, section 44 did not, in its 10 years of existence, lead to a single terrorist-related conviction.

The next area of threat, the internet and other instant forms of communications, was covered by the Regulation of Investigatory Powers Act. This enshrined into law the right of hundreds of public bodies (not just the intelligence services) to snoop on emails, phone calls and to film antisocial members of the public. The surveillance culture was known to be extensive. But it was only thanks to the Guardian's Prism revelations that the public finally understood that all communications were considered fair game.

Whenever challenged about the breadth of these powers, government ministers talk of checks and balances. None of these work properly: not parliament, not the courts, not ministerial accountability. Most MPs and peers do not have the technical knowledge to grasp the details of online surveillance. It's easy for the security agencies to run rings around them. Lawyers struggle to find out the facts as so much of the legal side of the security state is now held in secret. As for the politics, the government gives the police sweeping, vague powers and then says it cannot comment on operational issues.

Whitehall appears confident it can brazen out the Miranda controversy. Tuesday's response from the Home Office was instructive. If the police believed "an individual is in possession of highly sensitive stolen information that would help terrorism, then they should act and the law provides them with a framework to do that". The conflation is telling. The Prism revelations were detrimental to British and US government interest. They were, ipso facto, helpful to terrorists. The statement concluded with a perfect hint of menace: "Those who oppose this sort of action need to think about what they are condoning."

The next time you hear the Russians or Chinese, or any other authoritarian state, treating awkward critics as potential terrorists, and warning those worried by the security services' actions to back off, remember: we're pretty good at it too.

