The right does not want British institutions to take back control from the EU. It wants to take control of British institutions. Understand its raging ambition and you will understand why self-proclaimed Conservatives are so anxious to destroy.

Patriots who shout about their love of country daily announce their hatred of every British principle that might constrain them. The rule of law and sovereignty of parliament? The Mail echoed every totalitarian movement since the Jacobins and denounced judges as “enemies of the people” for ruling that Brexit couldn’t be triggered without the approval of parliament. Academic freedom? A government whip demanded universities tell him what lecturers were teaching about Brexit. The right of MPs to follow their conscience? Liberal Tories received death threats after the Telegraph called them “mutineers” for not obeying orders and thinking for themselves. Now the civil service is having its ethics besmirched and neutrality threatened. Jacob Rees-Mogg and Steve Baker accused it of plotting to undermine Brexit by producing needlessly pessimistic forecasts. The lie was so demonstrably false even Baker had to apologise. Tellingly, Rees-Mogg did not. Unnervingly, he may be our next prime minister.

You do not have to know much history to recognise a stab-in-the-back myth in the making. German militarists and fascists explained away defeat in the First World War with the dolchstosslegende: the German armies had not been defeated by their enemies in France but by communists, Jews and pacifists at home. So Brexit will not be defeated because the Tory right sold the British a fantasy but because judges, civil servants, saboteurs and mutineers subverted a glorious victory.

Far from holding back the growth of extremism, our leaders encourage it. The received wisdom holds that Theresa May does not know what she wants from Brexit. As my colleague Rafael Behr says, Mrs May has told us exactly what she wants. She wants Britain to walk away from the EU, its single market, customs union and courts, while retaining privileged access to its markets. The trouble with what she wants is not that she does not know it but that it’s impossible to achieve.

“We can have our cake and eat it” is no longer the slogan of that asinine opportunist Boris Johnson but of the post-Brexit establishment. Both Conservatives and Labour pretend there is no hard choice between taking back control and economic hardship. May tells the BBC we can have it all because that’s “what the British people voted for”. Presumably, if the British people voted for unicorns to deliver hot and cold running champagne, she would say they must have that too.

Rather than challenge her, Jeremy Corbyn echoes her. He insists we can leave the single market, while “retaining the benefits” of being in the single market. Brexit is performing a reverse alchemy on British parties, turning their golden principles into base metal. The Tories are threatening business. The anti-racist, pro-union Labour left still thinks it has the right to brand Labour leaders of the past as sell outs. Yet it sits on its hands as Corbyn maintains immigrants are wrecking job opportunities for natives and does nothing as he ignores the TUC’s warning that leaving the single market will threaten job security and workers’ rights.

Britain is a lucky country. It was on the winning side in two world wars and in the Cold War. Unlike virtually every other European, African and Asian state in the 20th century, we were never invaded or occupied. The British were the colonisers, not the colonised; the victors, not the vanquished.

British exceptionalism helps explain why 17.4 million voted to leave the EU. Countries with more tragic histories would never have taken such a reckless step. The smugness stability has given Britain has a further consequence. It makes it next to impossible to warn about the corruption of national life. Point to the Trumpian contempt for independent institutions, the impatience with checks and balances on power and disdain for truth and you are told to keep calm and carry on. These ills may afflict foreigners but they can’t happen here.

For all the complacency, cowardice still comes at a price – even in Britain. The cowardice of May and Corbyn is preparing the ground for a nationalist reaction to Brexit’s inevitable disappointment. Millions will find they can’t have it all and look for someone to blame. It is not alarmist to imagine a rightwing government deflecting attention from its own culpability and using conspiracy theory to justify attacks on the independence of the judiciary, civil service and BBC. A far-left government would be as eager to assault all three and replace neutral men and women with forelock-tugging ideologues. No one, indeed, should be more grateful to Rees-Mogg and the Daily Mail than John McDonnell. They are providing the ammunition he may reach for in office.

Britain might have voted to leave the EU, but it cannot leave the modern world. In Russia, Hungary, Poland, the US and Venezuela, we have seen elected autocrats sweeping aside, or attempting to sweep aside, constraints on their power. They have the people’s mandate. Anyone who stands in their way is therefore an enemy of democracy itself. We should look at countries where extremists, who bear a striking similarity to our extremists, are in power and remember that the past doesn’t determine the future. Just because it hasn’t happened here does not mean the British can console themselves with the happy thought that it can’t happen here – the more so when it already is.