The state has always wanted to know as much as it can about its citizens. Snooping is in its nature. Yet the fundamental assumption of the democratic era is that we should be free to live our lives privately and without interference, provided that we obey the law and do not pose a risk to others. So the issue that arises, in this trade-off between security and liberty, is how much of the latter we are prepared to give up so as not to jeopardise the former.
This is the judgment the Government is inviting all us to make with its plan to give the police and intelligence agencies instant access to our communications data. They will be able to find out to whom we are sending texts and emails; whom we are phoning and how often; which websites we visit; and even which video games we are playing online. This information will be stored by the internet service providers (ISPs), but can be accessed by the authorities in real time. One campaigner yesterday called it "a bug in every home".
Supporters justify these new powers as an essential counter-terrorism tool. They have cited the case of Mohammed Merah, the jihadist shot in Toulouse recently after killing seven people. But this is misleading: Merah was already known to French intelligence, and the fact that he wasn't stopped from embarking on his murderous spree had nothing to do with any limits placed on their surveillance capabilities.
Here in the UK, measures already exist to keep tabs on those suspected of wrongdoing, whether they be terrorists, paedophiles or bank robbers. The police or the security services can obtain warrants to tap phones, follow individuals, enter their homes and seize their computers. Under the EU Data Retention Directive, telecommunications operators and ISPs store information on a voluntary basis for 12 months. This can still identify the owner of a phone, whom they call, the duration of those conversations, and the approximate locations of both parties, though it does not include what exactly was said. And there's more. Banks keep information about financial transactions for seven years; postal data, such as recorded delivery details, are retained; and journeys by road are monitored using roadside cameras armed with automatic number-plate recognition technology.
In short, agencies of the state already have access to a mass of stored information about suspected bombers or paedophiles. What more do they need? The Government argues that communications technology is developing so quickly that it needs to keep pace with texting, Facebook and instant messaging. But this is not just about adapting to the rapidly changing world of the internet. A fundamental shift is being proposed, which alters the balance between security and liberty.
At the moment, there must be a reasonable suspicion that someone is up to no good before permission to snoop is granted - usually by a judge or senior minister. But from what we know about the latest proposal, due to be announced in the Queen's Speech, no such warrants would be required, allowing instant data-mining on a vast scale. The fictional world of Spooks, where an MI5 computer nerd at a desk in central London can track a terrorist suspect around the capital by tapping into CCTV, mobile phones and emails, would become a reality. As one campaigner says: "You will never know when you are being watched, and nobody else will either, because none of it will need a warrant." Effectively, it would allow a surveillance free-for-all in which the entire population of the country is treated as a pool of potential suspects.
Are we happy with that? When Labour proposed something identical in 2006, the parties now in Coalition were opposed; the Tories said they would judge any new powers against "the principles of proportionality and necessity". Now that they and the Lib Dems are in office - and have evidently changed their minds - the question that arises is whether this test has been met sufficiently to justify such a huge extension of the state's powers.
Not only will such a project be massively expensive and complex, but it would be of arguable benefit to the counter-terrorism effort. MI5 has a difficult job identifying potential terrorists if they never surface and use internet chatrooms to keep in touch. Some jihadists have even been known to hide their messages on paedophile sites, in the knowledge that other users are hardly likely to tip off the authorities. But is it sensible, when you are looking for a needle in a haystack, simply to increase the size of the haystack?
The other problem the Government faces is that it is not trusted to use these powers proportionately. The terrorism legislation introduced after 9/11 let the police stop and search people in designated areas without reasonable suspicion. But this was abused: hundreds of thousands of people were stopped by policemen looking for offences of any kind, on what effectively became fishing expeditions.
The same happened with the Regulation of Investigatory Powers Act, which gave dozens of organisations, including quangos, local authorities and government departments, the power to access communications data that had already been collected - using only their own authority to do so. These powers are now deployed more than half a million times a year - so why should we believe this latest measure will really be for our own good? Stopping us being blown up by crazed jihadists sounds like a compelling rationale. But we must judge it against what we already know of the state's irresistible compulsion to keep tabs on us all, simply because it can.