On 23 February 1820, a party of soldiers and watchmen swooped on a huddle of men in dingy quarters on Cato Street, near Edgware Road in London. There was a brief but desperate struggle by the light of guttering candles. Constable Smithers was run through with a well-aimed sword thrust by Arthur Thistlewood and died almost immediately, but the twenty or so men present were quickly taken into custody.

Within hours, the news spread. A grimy gang of desperadoes had been captured just in time to stop them setting out on an assassination plot of shocking audacity. They had been within minutes of descending on a house in Grosvenor Square where the entire Cabinet was expected to be sitting down for dinner. They intended to kill every man in the room, though not before making Lord Castlereagh, the most hated minister of all, beg for his life. They had planned to decapitate their victims with butcher’s knives and parade their heads on pikes through the streets of London. This, they hoped, would spark ‘confusion and anarchy’, as Thistlewood put it, out of which would somehow emerge a new government.

The conspirators had been played like fish on a line. Castlereagh crowed at how artfully the entrapment had worked out: ‘The whole has been arranged without a fault.’ The Cabinet dinner was a fiction. Its announcement had been planted in a newspaper and brought to the attention of Thistlewood and his confrères by George Edwards. On the face of it, Edwards – a model maker who sold plaster figurines of unpopular teachers for Eton schoolboys to smash – was the group’s most determined and enthusiastic proponent of bloody deeds. In reality, he was a spy in the pay of Lord Sidmouth, the home secretary.

Members of the captured terrorist cell were dragged before the ministers they had intended to kill for interrogation. A few days later, they were put on trial for high treason. The verdict was guilty, and before a large London crowd, five of them were hanged and their bodies beheaded.

The Cato Street conspirators had, in their own words, contemplated ‘murder in liberty’s cause’. Most people were horrified. There is no doubt, however, that many at the time would have favoured overthrowing the government through more honourable means. Britain was the top-ranking global power and industrialisation had made it the world’s economic powerhouse, but at the cost of severe social strains. For over ten years, popular frustration had been building. Luddite machine-breakers had conducted something like a guerrilla war in the North and Midlands, weavers had gone on strike and demonstrated around Manchester, and the London mob was tumultuous in its calls for electoral reform. With the end of the long war with France in 1815, patriotic appeals could no longer easily quieten opposition. Popular discontent with a seemingly permanent Tory government threatened to boil over.

While widespread support for revolution existed in the country, there was no clear strategy for bringing it about. Back in 1798, Castlereagh had helped prod the revolutionary United Irishmen into open rebellion, allowing the uprising to be brutally crushed. Radicals remembered and wondered how to avoid a similar debacle.

British revolutionaries put their faith in a more or less spontaneous uprising that would paralyse and disintegrate the forces of the state. The government was well aware of this and Sidmouth’s spy system worked to produce premature and isolated outbreaks that could be crushed expeditiously. A march on London from Manchester was dispersed by the military in March 1817. ‘Oliver the Spy’ cajoled three hundred labourers from Nottinghamshire and Derbyshire to march on Nottingham in June 1817, allowing them to be easily put down by cavalry.

Radicals increasingly turned to mass demonstrations, which, it was hoped, would spiral into general insurrection. The ultra-radicals of London, those who would later meet their doom at Cato Street, called a reform meeting on 2 December 1816 at London’s Spa Fields, Clerkenwell, and led off a section of the ten thousand in attendance to raid gun shops and march on the Tower of London. The rising was contained by soldiers and the leaders were put on trial for high treason, only for the prosecution to collapse when one of their number, John Castle, was exposed as a government spy and dissolute character (he was a bigamist and a brothel keeper).

When northern radicals organised a mass demonstration on Manchester’s Peter’s Field on 16 August 1819, the government treated it as a subversive threat to the state and gave the yeomanry and army carte blanche to deal with it. The result was the ‘Peterloo’ massacre in which eighteen people were martyred in the cause of liberty. An outraged public made a hero of Henry ‘Orator’ Hunt, the day’s headline speaker. In its aftermath, he travelled down the country, stopping repeatedly to address audiences made furious by the government’s cold-blooded repression.

Hunt’s reception in London on 13 September, organised by the ultra-radical veterans of the Spa Fields riot, was a tremendous success. Half the city turned out to watch him enter London and join the procession formed in his honour. Hunt took the opportunity to distance himself from the ultras, however, rejecting their insurrectionism and proto-socialism. He dismissed their proposal for simultaneous demonstrations across the country to stretch policing beyond breaking point. The ultras’ attempt to organise a rally at Finsbury Market without Hunt’s support proved an embarrassing failure. The government, meanwhile, passed the notorious Six Acts, which licensed a crackdown on seditious publications and meetings and unauthorised public drilling.

By 1820, the revolutionary moment had passed. Popular attention and sympathy were passing to the plight of Queen Caroline, wife of the new king, George IV, who hated and did his best to humiliate her. The ultra-radicals could no longer appeal to Hunt’s prestige and were incapable of organising the kind of mass protests that might conceivably spiral into popular revolution. Dr James Watson, their most capable leader, was imprisoned for debt and the direction of the group fell to Thistlewood, an irascible scapegrace of doubtful mental stability. Edwards the spy reported to his handler, ‘Thistlewood is the boy for us, he’s the one to do our work.’ Reduced to a small inward-looking core, the ultras were easily led into a fantasy of bloody revenge against a government that had checkmated them.

Taken together, the two trials of conspirators for treason produced a mass of evidence, and Vic Gatrell makes excellent use of it to write a psycho-history of men driven to distraction. His aim is to ‘establish a sense of human connection with those poor people’. Their putative victims, the ‘sadistic … aristocratic barbarians’, get shorter shrift. The Cato Street Conspiracy has been treated by most historians as a dead end in the long history of radicalism and the struggle for working-class representation. Gatrell dismisses such ‘forward march of labour’ historiography as passé and is more interested in exploring the emotional lives of his zealots for liberty.

Revolution, Gatrell argues, was impossible only because of the sheer reach and ruthlessness of the repressive state. This is perhaps doubtful: there were revolutions against generally much more brutal regimes in 1820 in Spain, Portugal and Italy. E P Thompson’s argument that the absence of middle-class solidarity with the working classes meant that a British revolution could not be carried off at this juncture still carries conviction.

The Cato Street Conspiracy in fact marked the final discrediting of outright repression and the spy system. When the middle and working classes did combine in 1832, the government decided that retreat was preferable to resistance and the Great Reform Act was carried. Workers remained discontented, but the problem of how to carry out revolution without middle-class support was not answered by the Chartists in the following decades. Britain failed either to invent barricade fighting or even to adopt it when it swept the Continent after 1830. The myth of Britain’s innate immunity to revolution became self-fulfilling in time, but Gatrell’s gripping study opens up a world in which the prospect seemed very real indeed.