What do you do when you know nobody can stop you? Me, I like to travel. In the past three years, I’ve been lucky enough to spend time in a number of world cities, but lately when I come back home to London and ride the Underground, I am struck by a nagging sense that something is missing. It took a friend visiting from the United States to point out what it is. There’s almost no graffiti. The people of London do not habitually doodle on our public transportation system. That makes us unusual.

It’s very hard to stop people writing on their own city. In Berlin, in New York and in Chicago, buses and trains and public buildings have tags and drawings scrawled all over them, from the skilled and serious to the crudely anatomical. This winter, in the streets outside the Ittihadiya Palace in Cairo, a bold slogan was daubed over the latest attempt by state officials to whitewash over words of protest. When I asked my friend to translate the Arabic, he told me it meant: “Hey, nice paint job!” In the Athens subway, every surface that will hold colour has been annotated. But not the London Underground, which coincidentally is watched by more than 11,000 CCTV cameras.

We have murals and bits of street art, but everyday graffiti is far less common than elsewhere. What is stopping us?

It’s not that Londoners are afraid. Not quite. It’s that in the world’s most surveillance-heavy metropolis, in a city that unironically welcomed tourists to the Olympics with a mascot of a lidless panopticon eyeball dressed as a police officer, it usually doesn’t occur to us to be anything other than compliant.

After the revelations in the past few weeks that the US National Security Agency and British intelligence have had access to data from big internet and telephone providers through the Prism programme, it is worth thinking about how everyday surveillance changes our behaviour. I’m not just talking about activists. I’m also talking to you, typical New Statesman reader, you who are the picture of moderate liberalism and have only occasionally contemplated setting fire to the House of Lords. As it becomes easier and more routine for states to collect and analyse large quantities of data about their citizens, and as it becomes ever harder for those citizens to stop them, the changes are producing a gradual chilling effect.

Don’t panic: just because Google, Facebook, Skype, Verizon and other companies are routinely monitored by the CIA doesn’t mean that somebody is watching you every time you order groceries online or voice-chat your sister in Seoul. It just means that they could if you gave them a reason to do so. That means you can relax – right up until the time when you want to go to a protest, or your sister does, or you support the fact that several thousand complete strangers did.

It’s hard to talk about all of this sensibly without sounding like the proverbial streetcorner ranter, two screws short of an inflammatory sandwich board, telling everyone how the CIA has put cameras in our underpants. The problem is that the CIA probably wouldput cameras in our underpants if there were a subtle, easy and cost-effective way for it to do so, although I pity the poor surveillance grunt who might one day have to check out where my Marks & Spencer value-pack knickers have been.

As it is, it has become dramatically easier to watch what people do from day to day on a very intimate level. We knew this before the NSA leaks. We are reminded of it every time we tick the little box that says “I agree”. The big question is how it changes our everyday behaviour.

There is a significant psychological price to being constantly aware of the variety of ways in which your activity might be tracked. To be blunt, it makes you feel crazy. That is why, if you want a quiet life, you shouldn’t make friends with security analysts: they tend to get drunk and describe the ways in which your phone can be turned into a listening device until the skin on the back of your neck starts to crawl, because it’s their job to know about such things. There is a non-zero cost to this sort of awareness.

In a choice between paranoid vigilance and easy participation, few choose paranoia. It’s just easier to change your behaviour. A friend who works in computer security told me that “the most important censorship happens between your head and your keyboard”. Self-censorship is significant in a world where, increasingly, as the tech journalist Quinn Norton observes, “falling in love, going to war and filling out tax forms looks the same: it looks like typing”.

There are still ways to operate in private. If I want to have an online conversation or make a transaction that I’m absolutely sure can’t be snooped on, there are tools I can download, software I can teach myself to use. But it’s a faff, and it can protect you only so far unless you choose to go entirely off-grid, and I’ve been addicted to Facebook since 2006. It’s far less trouble to modify your behaviour so you don’t ever say anything that might give the wrong impression. It’s easier, in short, to behave.

Fighting for the basic privacy that our grandparents took for granted is exhausting, so, instead, we might change how we speak and act, subtly, without even knowing that we’re doing it. The word that Michel Foucault uses to describe this type of modified behaviour is discipline. We might not make jokes about blowing up airports on the internet any longer, because we know that if we’re caught there will be consequences. We might not make any more unauthorised searches on our work computers. We might take care what we download.

The chilling disciplinary effect taking place in the digital age affects everyone. Whether we tolerate further intrusions on our privacy or continue to self-censor as a response to surveillance is up to all of us.