Boris Johnson and Rees-Mogg are populists. They affect to be all things to all people. They are simultaneously entertainers and politicians. They even evoke long past eras: dressing up in old-fashioned clothing, and affecting accents last heard in 1947. And they must be defeated.

There are two sides forming in British politics at the moment, between those who are interested in defending liberal democracy and those on the populist side who wish it harm.

Liberal democracy has a distinction between ethics and politics hardwired into its system, giving leeway for competing notions of the good. Politics (the way power is distributed in the public sphere) is kept apart from ethics (a sense of ‘what is good’ that emerges between individuals). Liberal democracy preserves pluralism in the public sphere.

Its absolutist enemies cannot stand pluralism. They affect to return democracy to an organic state where man meets his fellow man in a shared sense of goodness, of what is right.

Both the Left and the Right in this country have been captured by these groups who want to replace the normal run of politics with a transformative ethic, a vision of human relations transformed in light of ‘the good’, however broadly defined.

Just look at the language of Momentum on the Left. It promises ‘a new kind of politics’: “Momentum has over 150 local groups, 23,000 members and 200,000 supporters, united by their shared vision for a fair and equal society.”

Politics is turned into a game of active participation, of commitment and belief.

This has happened to the Right too. From Leave.EU’s manifesto for change: “We are taking back control of our sovereignty … We will now be able to take back control of our country.” Politics is enmeshed in a vision of control, of will. It is transformed into ‘real’ participation. It’s what lies behind behind Jacob Rees-Mogg’s attacks on the civil service – by illuminating the real costs and potential dilemmas of Brexit, it refused to join in with the ecstatic ethic of celebration that makes up the Brexiteer vision.

Liberal democracy seeks to contain and reflect competing visions of ‘the good’ by positioning the political sphere as a realm of tragic conflict, where values continually clash and merge into each other – forever incommensurable, forever unfulfilled.

Isaiah Berlin did the most to define British liberalism. For Berlin, Liberalism’s greatest enemies are those who challenge pluralism with a narrow interpretation of the collective good: “Single-minded monists, ruthless fanatics, men possessed by an all-embracing coherent vision do not know the doubts and agonies of those who cannot wholly blind themselves to reality.”

This profound sense that visions of the collective good are sometimes incompatible, that human beings are always enmeshed in tragic conflict, is the justifying ethos of liberal democracies: it’s also one of the reasons why we must fight to preserve them.

British politics is being eaten whole by its enemies. I was cheered today by Anna Soubry MP on BBC Newsnight, when she said: “If it comes to it, I am not going to stay in a party which has been taken over by the likes of Jacob Rees-Mogg and Boris Johnson. They are not proper Conservatives.”

Corbyn and Momentum have eaten the Labour Party whole. Historically, one of the open society’s defenders, Labour is now just another of the rabble that yearns for its end. The hard Brexiteers are doing the same to the Tory party. Don’t let them.