A bizarre trial begins on Monday at Blackfriars Crown Court. Its proceedings are predicted to last at least six weeks, and the costs — no doubt extravagant — will be largely borne by taxpayers. At the centre of this legal circus are a group of so-called “place-hackers”, people who get their kicks from gaining access to derelict, secret or otherwise off-limits parts of the city. In recent years such “urban explorers” have become increasingly bold in challenging the official demarcation of public versus private space in our city. These conflicting visions of urban space will clash during this trial.

Transport for London, in conjunction with the British Transport Police, has spent 20 months gathering evidence against the 12 accused, but the charge levelled against them is merely that they “conspired to commit criminal damage”. I can only assume that this is because, despite the lengthy investigation, the police have found insufficient evidence of actual damage, and so have resorted to prosecuting what’s effectively a thought-crime. Be that as it may, if convicted, the place-hackers may well receive lengthy prison sentences.

I’ve no doubt that TfL and the police are justifiably annoyed by the place-hackers’ antics. Entering abandoned Tube stations, the Crossrail tunnels, the old Post Office railway that runs beneath London — these are breaches of security, without doubt, but if any punishment is appropriate for such behaviour it’s some form of community service, not a jail term. These trespassers hurt nobody and damaged nothing, yet their doors were broken down with battering rams in the dead of night, and one of the defendants was arrested on the tarmac at Heathrow and hauled off his flight handcuffed.

I suspect the aggressiveness of the authorities’ response reflects a deeper level of anxiety about the city and the way we all live in it. For the most part we behave ourselves — we walk this way and not that, we stand on the right and go up the stairs on the left. Our movements about London are closely circumscribed, and while we may imagine ourselves to be free, the truth is that the vast majority of our journeys are undertaken for commercial imperatives: we travel either to work or to spend.

All about us during our daily existence we are presented with buildings we cannot enter, fences we cannot climb and thoroughfares it would be foolhardy to cross. We are disbarred from some places because we don’t have the money — and from others because we don’t have the power. The city promises us everything, but it will deliver only a bit.

The place-hackers draw our attention to how physically and commercially circumscribed our urban existence really is. Some of the defendants were involved in a daring ascent of the Shard while it was still under construction; others have trespassed in the great Modernist ruin of Battersea Power Station. In all cases, whether going up, down, or around, the place-hackers demonstrate a willingness to truly experience the city as it is, rather than be satisfied with the London that only comes with a price tag.

No doubt TfL feels it’s necessary to obtain a conviction pour encourager les autres. But the paradox is that in my experience it’s extremely hard to get Londoners to step outside their comfort zone and take a walk on the wild side: we’re mostly too tired from all that grafting and commuting. I don’t think we have to go to the extreme of climbing the Shard or plumbing the depths of Bazalgette’s sewers, but surely we should be able to enjoy more of the city than simply its paid-for “attractions” and “legacy” parks?

What makes the trial even more bizarre is that one of the defendants, Dr Bradley Garrett, is a respected academic at Oxford University whose doctoral thesis was written on… place-hacking. Dr Garrett was working in the tradition of ethnographers from Malinowski to Margaret Meade when he joined the place-hackers on their nocturnal adventures. He has subsequently published a book, Explore Everything, that examines urban exploration as a subcultural activity and an active critique of our increasingly off-limits city. Needless to say, TfL attempted to prevent its publication, showing a commitment to suppressing scholarship that goes, I would say, rather beyond its remit.

As more and more international capital flows into London, so public space is increasingly eroded — it’s just too valuable for us ordinary folk to paddle about in any more. The place-hackers demonstrate what happens when property rights of any sort are challenged: the law comes down on you like a ton of London stock bricks. But one of the many ironies in this imbroglio is that almost all of the sites they entered have now become valuable real estate: it’s as if the place-hackers’ derring-do made these abandoned bunkers and sealed-up tunnels appear sexier and more marketable than heretofore.

It also seems likely that at least part of the Crown’s case against the place-hackers will be based on appeal to security issues: by getting into the culverts housing communications cabling, or the sewers washing away our effluvium, then posting images online of themselves doing so, surely the place-hackers are putting ideas into the heads of those with violent agendas? Maybe —but somehow I doubt it. Terrorists aim to achieve maximum body counts and to galvanise the media through spectacular acts, but there’s not much publicity to be gained by going into abandoned buildings. The last major terrorist attack in London happened on ordinary buses and Tubes that were by no means off-limits.

I personally believe place-hackers are performing a valuable service by reminding us that the city should, in principle, belong to its citizens, and should mostly — if not entirely — be accessible to them. I don’t expect everyone to be as radical as me on this point but surely public money would be better spent on improving our transport infrastructure rather than prosecuting a group of harmless eccentrics for the thought-crime of possibly damaging it.