Mies van der Rohe's unbuilt London tower would have been more than a modernist icon, it would have created the only useable space for protest in the City of London, says Jack Self in this Opinion column.

For the first time in more than 30 years, Mies van der Rohe's only UK project is being presented to the public – in both a forthcoming exhibition at the RIBA and, if it is successful, a book funded through Kickstarter by the REAL Foundation.

Alternatively referred to by Prince Charles as "a giant glass stump" and Richard Rogers as "the culmination of a master architect's life work", Mies' unbuilt Mansion House Square remains highly controversial, even 50 years after its conception. The project's failure to be realised is often blamed on a massive mood swing in the UK concerning how the public viewed modernist architecture.

It is true that when the scheme was finally cancelled in the mid 1980s, it was right at the moment when historical pastiche and an obsession with preservation overthrew the postwar, predominantly brutalist paradigm – one that was increasingly associated with social dystopias, not social democracy.

But is that myth actually true? Did the British really come to hate modernism generally and corporate modernist towers specifically? If so, how can we explain the explosion of precisely this type of building in the subsequent decades all around the City, from Lloyd's of London to the Gherkin or Cheesegrater? Was there perhaps another quality about Mies' project, aside from its modernist aesthetic, that made it politically impossible to build?

Mies took a scrambled, dangerous street pattern and rationalised it with a perfect grid

A key element to the scheme was the creation of a large public square to the east of the site, adjacent to the City Mayor's residence Mansion House. In some respects, this space was the greatest genius of the scheme. Mies took a scrambled, dangerous street pattern surrounding the Bank of England and (apparently effortlessly) rationalised it with a perfect grid.

This move carved out a serene ceremonial area directly in front of one of London's most important seats of power, which remains rather claustrophobically oppressed by its neighbours to this day. Such a generous civic gesture was not flagged as problematic when planning was granted in the mid 1960s, precisely because it was such an unquestionably positive addition to London. However, by the mid 1980s this public space had become a real source of panic for both the City and the British government.

The 1980s were a famously tumultuous decade for the UK, as Thatcherite reforms radically transformed the structure of employment and basic fabric of society. Strikes and civil unrest in London were common, from dockworker and printers' union disputes in the east to violent race riots in Brixton and deadly anti-government protests in Trafalgar Square. Thrown into this mix were IRA bomb attacks, which at their worst point occurred almost every month (one of my earliest memories is being caught up in a blast at John Lewis on Oxford Street).

Large crowds – whether gathered out of civic pride or civil disobedience – were no longer universally desirable in the city. Public space had become dangerous.

This public space became a real source of panic for both the City and the British government

It is important to keep in mind that, by the mid 1980s, powerful components of neoliberal ideology had embedded themselves within the internal logic of governance. Some of these principles were that there was no such thing as society; that there was no alternative to deregulated free markets; that the state was an inherently wasteful, inefficient and unprofitable entity; and, therefore, its scope should be reduced by privatisation and corporatisation wherever possible.

Although Margaret Thatcher was extremely popular, she was also extremely divisive, and the large minority of people that opposed her were restive and vocal. There was a widespread belief amongst those in power that the basic functions of the nation faced existential threats from the protest, dissidence and unrest.

The responses by urban policy-makers to these problems of civic security were twofold. They prevented the formation of new public spaces wherever they could, often through blocking new development on ground of "historical merit", and they installed various devices in existing spaces to limit their capacity and control their crowds. Mies' project, Mansion House Square, may have been simply too generous, and more than the City could accept.

In 1848, during a comparable period of social upheaval in Britain, London's authorities had installed two massive fountains into Trafalgar Square, to halve the number of people that could congregate there. Some time later, crude chains were added. Then the adjacent roads were redirected in such a way as to make the square into a kind of traffic island. These innovations became the basis for most anti-protest, anti-terror strategies that – until today – remain central to the governance of London's public spaces.

The mechanisms are as diverse as they are ingenious. There are simple barriers, railings and gates. There are tools that rely on social norms (taking advantage of the British tendency toward polite obedience), such as excessive signage, road and pavement markings, or brass plugs in the pavement delineating private ownership. And then there are the urban tactics that coerce and influence in an unseen way: sophisticated anti-bomb bollards disguised as benches, water features like moats and fountains, lanes of traffic that encircle crowds like sheepdogs herding a flock.

We are told that these measures are necessary for our own protection. However, in broader historical terms it is not the public that really has to worry about terrorism. It is the authorities that must manage the risk of civil disobedience.

If Mies' square had been completed it would have been an ideal locus for Occupy

The current state of public space, particularly in the City of London, bears testament to this fear. In October 2011 I joined a Facebook group calling itself Occupy London, and a few days later – when it announced a march – I fashioned the wittiest anti-capitalist sign I could think of and went down to the Stock Exchange.

As the crowd twisted along its route I found myself progressively shuffled towards the front, and as we arrived at our destination I was nearly cheek-to-cheek with a phalanx of anti-riot police. The London Stock Exchange (LSX), which at that time was majority controlled by Toshiba, is located opposite St Paul's Cathedral, in a privately owned complex called Pater Noster Square. Because of this there was no way to "occupy" LSX and we were halted short of the target.

In fact, there was no way to occupy anything else in the City either – within a few days the City issued a memo advising companies to regularly check any nearby vacant properties for squatters, and instructed them to block access to all corporately controlled, publicly accessible spaces until further notice. The only exception was St Paul's Churchyard, over which they did not hold such direct control. So Occupy claimed sanctuary there. We established a tent city, a library, a "university." I even spent a night camping on the steps before the cathedral authorities were eventually pressured by the City to evict the protesters and dismantle the camp.

In a post-Trump, post-Brexit reality, public space and its occupation have never seemed so relevant

If Mies' square had been completed it would have been an ideal locus for Occupy, which as a civic function is without doubt a positive contribution to the health of British democracy. But more importantly, for the overwhelming majority of the time when people are not setting up soup kitchens or hand-stitching banners, it would have been a wonderful public amenity.

Mies' Mansion House Square scheme is the greatest public space never to have been built in London.

This is precisely why I have been so motivated to make the project available to the public. Me and the REAL foundation have spent almost two years working closely with the building's commissioner, Lord Palumbo, as well as the RIBA (who are planning an exhibition on Mansion House Square and James Stirling's One Poultry to open in March) with the aim of publishing a wide variety of project documents.

In a post-Trump, post-Brexit reality, public space and its occupation have never seemed so relevant. It is my strong hope that, by shining more light onto Mies' attempted intervention in London, we can contribute to a renewed debate about what type of cities we want to live in today.