Douglas Carswell does not record exactly when he decided that Nigel Farage was a charlatan. The epiphany is curiously vague in a book that combines personal memoir and political theory. In 2015, Carswell stood for parliament on a manifesto with Farage’s mirthless grin on its opening page. Yet, in Rebel, Carswell calls the man he once accepted as his leader a purveyor of “pound-shop populism”.

Did that insight elude him when he left the Conservatives to join Ukip in 2014 or, as his narrative implies but doesn’t quite declare, was he saving the revelation for an opportune moment? On the eve of his book’s publication, Carswell quit Ukip and declared himself independent of party allegiance.

He now sees Farage, alongside Donald Trump, Marine Le Pen and Jeremy Corbyn, as part of a “New Radical” phenomenon. Their success is born of reaction against moral and financial corruption at the heart of western democracies. But, Carswell says, these figures are symptoms of the ailment, not its cure. They dig channels down which grievance flows but they lack vision of a better society. They have not understood the causes of their success, so their movements will misfire. Rebel is offered up as the missing remedy.

There is a remarkable breadth of history in this book, ranging from ancient Greece to the present day. It is a feat of organisation and stylistic brio to pull so much into a short volume that motors along jauntily, without crunching of gears. The author deserves credit for the scale of his ambition and sustained narrative energy, but there is a cost in credibility.

Carswell’s urgency precludes subtlety and self-doubt. His imminent concern is that western democracies could succumb to tyranny. This threat he sees not in the rise of Trump and his ilk but in the backlash against them. The danger is not in the thing that looks, to the naked eye, like fascism but in counter-revolution by an elite that despises the ordinary people who vote for fascistic candidates. The old ruling oligarchy will use the incompetence of the New Radicals to justify an assault on democracy. With this twist of rhetorical jujitsu, Carswell turns the anxiety of anti-Trump liberals and EU remainers against them. Their fear of aggressive nationalism becomes the real aggressor.

This requires some selective history. It means, for example, casting Vote Leave, the official campaign against EU membership, as the victim of last year’s referendum: a plucky rebellion, noble in manner and intent, traduced by media bias. He sees the purity of their cause uncontaminated by flecks of grubby xenophobia peddled by the wrong sort of Eurosceptic. He finds ample room for ad hominem criticism of BBC journalists and yet, among many disquisitions on unaccountable corporations and partisan journalism, there is no mention of News Corp or Rupert Murdoch.

Ideological revisions always sand away awkward knots to make smooth polemical edges. Rebel is no exception. Carswell has a theory of what constitutes successful civilisation, involving free, mutual exchange of goods, decentralised politics and an absence of monopolising elites. He has surveyed the world and concluded that its story is a cycle of “constant conflict between those who produce and those who parasitise and predate”. He then makes various societies conform to the model. So the good guys – Republican Romans; 17th-century Dutch traders; US founding fathers – have common features leading to freedom and prosperity. The enemy is the greedy wrecker class that captures wealth and suffocates the sources of its creation.

Often the parable works, but it requires a glibness that is the enemy of scholarship. Religious persecutions, subordination of women and racial prejudice are minor foibles if they feature in societies that, in other respects, meet the criteria for success. “But, alongside slavery, Rome had a free labour market,” Carswell writes. Even when dealing with the horrors of the 20th century, Rebel steers condemnation of the Nazis towards their state-heavy corporatism, as if that is the salient feature of their wickedness.

Carswell does not waste time on definitions. There is a passage early on that sketches “Davos Man” as the private-jetting billionaire enemy of ordinary folk. This figure then morphs into a wider class of professionals: bankers, lawyers, politicians, journalists, academics, charity bosses and their urbane fellow travellers. Soon we are tilting at a row of oligarchic windmills that might represent anyone who voted to remain in the EU or who thought Hillary Clinton would have been an OK choice for US president.

This disregard for the nuance of political sympathy undoes the merit in Carswell’s arguments. He makes a good case for reforming the electoral system. He is insightful on the perils of groupthink and on the need for a doctrine of “fallibilism” that recognises the need for evidence-led policymaking. Yet he exudes unwavering confidence in his own infallibility.

When so much is crammed into so few pages, deformations are inevitable. But Carswell does not even pause to apologise for the damage. He is too busy making disparate connections, a bend here, a twist there, to complete the story. This approach, selecting useful facts, discarding inconvenient ones, holding it all up to the light at just the right angle, is standard polemical fare. But it is also the idiom of paranoid conspiracy theory. Rebel stays on the right side of that line. The denunciation of parasites is always metaphorical. Carswell does not posit some secret club of vampire-Illuminati sucking the lifeblood of trade freedom, but his style comes close.

At root this flows from the author’s determination to cast himself as the perpetual outsider. Even when sitting in the House of Commons he describes feelings of alienation from the clubby atmosphere. He has joined and left two political parties. He was part of the victorious campaign to take the UK out of the EU yet writes as if it was a defeat. These are the traits of a man who does not want responsibility. He wants to own the elegant vision, not the complex outcome. He wants to be followed, but never blamed. He draws energy from the failings of politics but does not want to be considered part of politics. A selective kind of analysis could make that sound rather parasitic.