I was recently sent a link to a YouTube video entitled We Too, in which a trespasser sneaks into the under-construction, 34-storey Lexicon skyscraper near the Silicon Roundabout in London, and pitches a tent on the top floor.

In the video, after a good night’s sleep, the interloper unzips the front flap of the shelter and steps into the early-morning air. The city unfolds before him in a stunning vista, suggesting the view that future occupants of the skyscraper will enjoy – or, more likely in London, the view that international investors will use as a selling point when they put the flat back on the market after a few years of not living in it.

Later that day, I received another link to Craigslist where the Lexicon lurker, as I came to call him, had placed an ad for a “highly affordable luxury penthouse in Islington”, illustrated with a crisp photo of his tent overlooking the city. The punchline of this performance – that “we too sleep in penthouses” – was a playful way of reframing the most pressing concern in the neoliberal city: who is it actually for?

The geographer David Harvey once wrote that “the freedom to make and remake our cities and ourselves is … one of the most precious yet most neglected of our human rights”. Generations of urban theorists, from Lewis Mumford to Jane Jacobs to Doreen Massey, have suggested that the place where cities get “remade” is in the public rather than private sphere. Part of the problem, then, with privately owned public spaces (“Pops”) – open-air squares, gardens and parks that look public but are not – is that the rights of the citizens using them are severely hemmed in. Although this issue might be academic while we’re eating our lunch on a private park bench, the consequences of multiplying and expanding Pops affects everything from our personal psyche to our ability to protest.

Let me offer two examples from other cities. I am originally from Los Angeles and recently went back to visit. When I asked an old friend where you could find the public space in LA, his response was: “What, to buy?” This sounds like sarcasm, but Los Angeles is a city infamous for slaying public space and public transportation. My friend clarified his genuine confusion later when he sent me a Los Angeles Times article about how the city had begun to sell slivers of pavement on the private market intended for crafty entrepreneurs looking for ad space.

So there’s one model – and here’s another. A few years back, I was in Phnom Penh, Cambodia, and I asked a colleague if we could go somewhere photogenic. I was taken to Vann Molyvann’s 1964 National Stadium, a Brutalist behemoth built in anticipation of the Southeast Asian Peninsular Games in 1963.

When we arrived, the place was filled with hundreds of people, none that I could see in any sort of official capacity. Some were conducting open-air aerobics classes, others were selling barbecued corn from rolling carts, a few people were air-drying laundry and many were just milling about on foot or scooters. I even met a child taking a bath in a bucket, who tried to douse me. Nothing was locked. I went in and out of areas at will, including the vast indoor stadium, which was unoccupied except for a few kids smoking a joint. There was an intense energy in the air that came from a little sprinkling of chaos – a feeling that anything could happen here.

It was then I realised that one problem with Pops is they lack that kind of energy. They feel too monitored, too controlled, to allow this communal activity to simply unfold. London, and many other cities, are failing miserably to enable diversity in people’s engagement with such spaces.

In 2012, the Guardian ran a campaign to crowdsource data about Pops in Britain. The project, though incomplete, suggested a clear pattern. Having begun to be built in the 1980s (unsurprisingly), Pops around the country increased steadily in number through the 2000s, and also grew in size. This includes the estate of More London, a 13-acre expanse stretching down the Thames’s Southbank. It was completed in 2003 and sold off in 2013 to Kuwaiti property company St Martins for £1.7bn, in one of the largest commercial property deals in British history.

In the process, the transformation of the areas outside City Hall into a Pops means it is no longer possible to protest outside the headquarters of the mayor and the Greater London Authority (GLA). Or to take photos, apparently: when I was filming with Channel 4 there last year, we were swiftly removed from the property. This is nothing new. In 2010, during a London Assembly planning and housing committee meeting, Jenny Jones, from the Green party, said: “It has taken us eight years to negotiate with More London so that we politicians can do a TV interview outside our own building.”

Despite multiple objections from politicians and notwithstanding Boris Johnson’s 2011 Manifesto for Public Space, the construction of Pops such as More London is continuing to escalate and expand, including nine acres planned in Tower Hamlets, a vast patch outside the Battersea Power Station development, and open space and parks at Woodberry Down near Manor House, where I was chased around for taking photos a few months ago. Given how all these developments seem to contradict stated city authority goals to increase public space that is actually publicly owned, one could be forgiven for thinking that the GLA is not actually in control of development in London.

So what is it we expect to happen in public space? In 2008, geographer Ash Amin wrote that “public spaces marked by the unfettered circulation of bodies [produce] new rhythms from the many relational possibilities”. I experienced elements of this in the Phnom Penh National Stadium. But, when space is controlled, and especially when the public is unclear about what the legal or acceptable boundaries of activity are, we tend to police ourselves, to monitor our behaviour and to limit our interactions, especially after embarrassing confrontations with security.

Property owners are perfectly aware of this and prey on those sensibilities. The new King’s Cross development at Granary Square is one of the largest open-air spaces in Europe – about the same size as Trafalgar Square. Unlike Trafalgar Square, it is also a Pops. Photographer Nicholas Goodden set up a tripod there recently to take a photo, and was immediately asked by security whether he had a permit to do so. When he said he did not, he was ordered to move across the canal to get his image. In other words, he was kicked out of “public” space. This would not have happened to a photojournalist in Trafalgar Square, which is owned by the Crown and managed by the Greater London Authority.

Moreover, an encounter with security like this may make you wary and cause you to confine your behaviour to a narrow range so as to avoid confrontation. The psychological effects of this sort of self-policing were written about by Michel Foucault: “He who is subjected to a field of visibility, and who knows it, assumes responsibility for the constraints of power; he makes them play spontaneously upon himself; he inscribes in himself the power relation in which he simultaneously plays both roles; he becomes the principle of his own subjection.”

Geographer Don Mitchell suggests that what public space provides in a city under surveillance are small islands of freedom surrounded by Foucault’s “carceral archipelago” – the surveilled city. Herein lies a crucial question: what happens when our small islands of freedom become indistinguishable from the rest of the city? Sociologist Richard Sennett suggests that private public spaces are “dead public spaces” because the essence of conviviality, spontaneity, encounter and yes, that little sprinkle of chaos, have been stripped out. The spaces are not rendered dead because they aren’t enjoyable – I myself enjoy lounging on the steps near the canal at Granary Square – but dead because the potential range of spatial engagement here can fit in a coffee cup.

“By claiming space in public, by creating public spaces, social groups themselves become public,” Mitchell writes. “Only in public spaces can the homeless, for example, represent themselves as a legitimate part of ‘the public’.” I’m sure we can all imagine how Granary Square security might respond to a homeless Londoner making their woes public on their private AstroTurf.

The power for corporate entities to not only impede certain activities but to bar the public access to “public” space was upheld during the Occupy protest court proceedings. On 14 October 2011, an injunction passed “preventing ‘persons unknown’ entering or remaining in or trespassing on [Paternoster Square]”. While Occupy may seem like ancient history, these proceedings were important because they set a precedent: protest would not be tolerated in open-air private space.

It is no coincidence that the aforementioned Lexicon lurker deployed a tent in his bogus ad. The tent has become a powerful totem: from Brian Haw to Occupy, it symbolises the bringing of the domestic sphere into the public, and has become so feared by authorities that Westminster City Council passed bylaws in 2012 “to regulate tents and other structures and sleeping equipment”. So much for urban camping.

At a recent TEDx Southampton University event about public space in London, I suggested that the moment for direct action against the loss of public space is upon us – an action that would echo the mass trespass of Kinder Scout by the Rambler’s Association in 1932, described by Lord Roy Hattersley as “the most successful direct action in British history”. Taking action by finding and using public space sidesteps the thorny, and frankly depressing, issue of what has been lost. Instead, it focuses on what we can do.

The first hurdle, however, is that public space in London has not been mapped in any sort of systematic way. Oliver Dawkins, doing degree work at UCL’s Centre for Advanced Spatial Analysis (Casa), created a “Pops Profiler” that enables us to see how this plays out in the Square Mile. Publicly available data on Open Street Maps (OSM) do not indicate a single open space that is explicitly designated as publicly accessible (though there are many where ownership is “unspecified”). This suggests that OSM users can’t tell which open spaces are public and which are private.

Last year, when I tried to walk a section of the Thames Path with Jack Shenker and Anna Minton, we found many underutilised parts of the trail – including one that a building security guard asked for identification to access. Hostile architecture intimidates people away from access, poor signage misdirects them. What I suggest in my TEDx talk is that we should start systematically mapping out and using these public spaces to raise awareness about what we have – before we lose it.

So that’s my plan. Along the way, in a series of articles for Guardian Cities, I intend to tackle overarching questions about where public spaces are, and what they are for. I am also interested in the ways that people subvert private space by undertaking “public” acts without permission, to create what Hakim Bey calls “temporary autonomous zones”. The deployment of the tent on Lexicon Tower is a good example of that.

As an ethnographer, I am keen to approach this project from the ground up, seeking out small acts and helping to organise events in public spaces. The fundamental question for me is one of visibility. If information about public space – where it is, what we can do in it – is not clear, then small acts can reveal what is and is not possible ... which we can then map. If you have a story you would like to share for inclusion in future pieces, please do get in touch.

Share your experience of how public space in cities is changing in the comments below, or by emailing cities@theguardian.com

• This article was amended on 6 August to clarify that accredited photojournalists (as opposed to all commercial photographers) do not require prior authorisation from the Greater London Authority to take photographs in Trafalgar Square, as detailed in the GLA byelaws.