It was a true year of revolution. In 1973, Londoners, for the first time in their modern history, had taken direct action against those purporting to rule them and scored a signal victory. It was an event that had more impact on the face of the capital than any since the great fire of London.

The genesis of the battle lay in an extraordinary plan from the academic Patrick Abercrombie, who was called in to advise the government on how to rebuild London from the ruins of war. Steeped in the modernist ideology of the French architect Le Corbusier, he felt that Britain’s victory over Hitler should signal the start of a utopian new age. London quite simply should be rebuilt afresh.

Abercrombie saw a city largely composed of “obsolete, bad, unsuitable” buildings. Apart from some “villages” such as Kensington, Hampstead or Hackney, it should be refashioned for the age of the motor car, built around five ring motorways and radials. Similar pre-war plans published by the Mars group of young architects depicted a London landscape entirely cleared of its existing districts, other than landmark monuments, such as the Houses of Parliament and the British Museum. The city would be one of rows of slabs and towers, similar to Corbusier’s plan for a new Paris of 60-storey towers.

Town planner and architect Prof Patrick Abercrombie. Photograph: Hulton Archive/Getty

Abercrombie’s proposals morphed into the London Plan to be adopted by the government and the London county council. The only dissenter was the City Corporation, which wanted a mini-motorway around its own boundary. Part of this was built as the present street called London Wall, first named Route Eleven. The plan was galvanised by a 1963 report on traffic in towns by the transport expert Colin Buchanan. He declared the prevailing principle of “traffic separation”, with cities designed around networks of urban motorways. Pedestrians would be elevated on to decks above which would rise estates of towers and slabs. The first (and virtually only) application of such separation was to be the Barbican in the City, which began construction in 1965.

By the 1970s, the Abercrombie plan was stumbling as ad hoc deals were reached between developers and local planners. But it remained the guide for all strategic planning decisions. Most controversial was its inner ring, the Motorway Box, intended to crash through Islington, Camden, Kensington, Clapham and Greenwich. On one count it would demolish more houses than did the Luftwaffe, requiring the rehousing of 100,000 people. Public meetings along its route were chaotic, with officials often having to run for cover. When the roads minister, none other than a young Michael Heseltine, opened the Westway link to the box over Notting Hill in 1970, he encountered a riot of abuse from infuriated residents, who had his motorway passing just feet from their bedroom windows.

The cost of decking central London would be astronomical – none of Abercrombie was costed or budgeted. Its economic viability was questioned when it was discovered that not one of the shop tenancies on the Barbican decks were sold, as they have not been to this day. Meanwhile, road widening became an obsession, with new houses and shops being forced back from street frontages to make room for more traffic, further reducing London’s already low housing density.

Angry local residents surround Michael Heseltine, then parliamentary secretary at the Ministry of Transport, as he opens the Westway, a 2.5 mile-long road that runs from Marylebone to Shepherd’s Bush. Photograph: PA Media

At the same time, Abercrombie’s new council housing estates were turning sour. The slabs of Pimlico’s Churchill Gardens started development in 1946 and were followed by a rash of towers across the south and east of London, in no case designed to protect or replicate the settled, mostly working-class neighbourhoods they destroyed. This community destruction, vividly recorded in 1950s Bethnal Green by the sociologists Willmott and Young, turned opinion against putting families in towers. This was dramatically exacerbated in 1968 with the collapse of the 22-storey Ronan Point in Canning Town, which left four dead. The government halted all new residential towers.

Each aspect of the London plan was now encountering political headwinds. Furious protests greeted an attempt – the second since the second world war – to demolish Piccadilly Circus as a traffic bottleneck and replace it with another Centre Point, the 33-storey tower block on the corner of Oxford Street and Charing Cross Road. The proposal was withdrawn, bizarrely, for not providing space for enough traffic.

The greatest battle was a 1968 plan from the new Greater London council (GLC) to flatten most of Covent Garden. A new estate would run from the Strand to Holborn composed of a second Barbican deck. (A relic of its false start can be seen at the top end of Drury Lane.) At the time, the area largely consisted of disused market warehouses, mansion blocks and a gentrifying scatter of new residents, many with a passionate commitment to its salvation. It was not a traditional working-class district, the likes of which planners had grown used to sweeping aside.

A militant community association sprang into action. Buildings were squatted, council meetings disrupted, streets occupied and councillors lobbied – or harassed. A renegade GLC official, Brian Anson, led the charge, appalled by the destruction and human dislocation of the plan he was expected to implement. He was joined by a young activist Jim Monahan and the vicar of nearby St Martin-in-the-Fields, Austen Williams.

The group was publicly supported by a then-radical Evening Standard, and by a wider awareness that a familiar London was being threatened by change more drastic than any inflicted by the blitz. It seemed at the mercy of a top-down ideology more typical of eastern Europe, one that ruled that the motor vehicle and its uses should be the dominant consideration of city planning. Eager young architects described it as “traffic modernism”.

The Tory government of Edward Heath was favourable to the plan and the GLC fought on through a rowdy public inquiry in 1971. Its traffic engineers proposed to turn the Strand and High Holborn into four-lane dual-carriageways, asserting that without them “London will grind to a halt”. The inquiry approved the plan, as did the government.

Despite continued protest through 1972, the Covent Garden plan pressed ahead. But trouble began when its custodian as GLC committee chairman, Lady Dartmouth (later Princess Diana’s stepmother, Lady Spencer), rebelled and joined the protesters. More critically, a sympathetic planning minister, Geoffrey Rippon, had his officials secretly list for preservation 250 “historic” buildings dotted across the entire plan area. When this became public, it sabotaged the entire proposal.

The GLC elections of 1973 saw the London Tories voted out of office. Labour councillors, who had previously supported the principles of Abercrombie and Buchanan, read the writing on the wall. The Covent Garden plan was abandoned. At the same time, the Motorway Box was formally dropped, releasing thousands of houses from planning blight. The Piccadilly tower was declared dead and the Circus safe. Central and local government alike got the message.

The effect of the revolution was astonishing – and to the best of my knowledge never fully acknowledged. Ministers also abandoned a proposal to demolish the entire government quarter of Whitehall from Downing Street to the river as far as the Houses of Parliament. The Foreign Office and Treasury would go. There was even a plan to pull down the whole of Carlton House Terrace overlooking St James’s Park for new office blocks.

All this was now put on hold. The mood shifted to other parts of London. The decking of Oxford Street died a death. St Pancras station survived British Rail’s proposal to demolish it, following the recent loss of the old Euston station. A frantic bout of listing narrowly saved the Georgian Spitalfields area immediately east of the City.

Abercrombie was over. The GLC and the London boroughs switched the outlook of their planning policies. They actively promoted the new 1967 Civic Amenities Act, allowing for the designation of conservation areas across Britain’s inner cities. By 1975, 250 such areas of mostly Georgian and Victorian streets had been given protection, including most of Westminster, Kensington and Chelsea and much of inner Camden and Islington. The appearance of inner London we see today was largely determined in the immediate aftermath of 1973.

Had it not been for an essentially political change of heart by the GLC and Whitehall, what are now some of the liveliest and most dynamic quarters of London would have been neutered. It is to the battles of the 1970s that we owe the survival of such colourful and diverse areas as Soho, Fitzrovia, Clerkenwell, Shoreditch, Bermondsey, Kennington and Clapham.

At the time, the zeal of architectural modernism was all-consuming. Many cities outside London, such as Newcastle, Liverpool, Bradford, Birmingham and Plymouth, saw sections of their mostly Victorian historic centres lost to comprehensive redevelopment. London, too, had its losses, such as the old Whitechapel, Elephant and Castle and Vauxhall. The loss was not just in collective memory and aesthetic appeal. What Covent Garden showed was that sensitive conservation lay at the root of economic dynamism and revival. The postwar demolition of much of the East End halted what should have been the spread eastwards of the economic renaissance of modern Hackney. It was not the blitz that killed the old East End, it was the planners.

The aftermath of the gas explosion at Ronan Point in Canning Town in 1968. Photograph: David Graves/Rex/Shutterstock

What saved Covent Garden from its fate was that the potential victims had enough fire in their bellies to fight back. The battles were often painful, the rows between activists, often from very different backgrounds, leading to many a pub bust-up. These were vividly chronicled by Brian Anson, in his pugnacious memoir, I’ll Fight You for It. City centre neighbourhoods are diverse in their inhabitants. Long-standing residents jostle with newcomers, often with conflicting demands. But at Covent Garden they had one goal in common, that the physical fabric of a city had a value that should be guarded for future as well as present generations, whatever their class or origins.

It is hard walking today through the teeming streets of Long Acre and Bow Street, Maiden Lane and Leicester Square, to imagine that London’s governors once wanted it all flattened. Talking years afterwards to those who had worked in County Hall at the time, I found them curiously numb. I asked a former councillor if he really would have preferred Covent Garden to be like the Barbican. He could only reply that: “The planners told us it was the future.”

It is the architecture profession, back to Abercrombie, that should be held responsible for what almost happened to London. We can blame elected politicians for decisions that govern our lives. But in complex decisions like this – as in matters of law, medicine or defence – they are at the mercy of professional experts. Architecture at the time had gone awry, seized by ideological gigantism, dubbed by some critics as an “edifice complex”. But I know of no effort by the profession to reflect on that period in its history, to set the record straight or show what lessons it has learned. It is now embarked on a similar mania, to build as many speculative luxury towers as it can before that boom burns out.

The way to prevent future Covent Gardens can only be to remain alert and to empower local people, not believe that some ordained future is inevitable. They can decide these things for themselves. It is the very essence of democracy.

Simon Jenkins’ A Short History of London: The Creation of a World Capital is published this week by Penguin. To order a copy for £18.65, go to guardianbookshop.com