Chris Grayling is Leader of the House of Commons, and MP for Epsom and Ewell.

Imagine that a new political party has emerged in the UK. Its activists are accused of anti-Semitic behaviour. On the doorsteps, it is said to have launched anti-Semitic attacks against Jewish candidates from other parties. The Party holds meetings at which men and women are segregated. It sets up a “compliance unit” to vet new applicants for membership, and then admits people who have urged ISIS to attack Israel, who say that the 9/11 suicide bombers should never be condemned, and who say that Remembrance events are “like murderers holding special funerals for their victims”. How should we describe such a Party?

Easy. The Labour Party.

The rapid march of the Labour Party towards the kind of extremism that should have no place in a modern society is alarming. Hardly a day seems to go by without another story emerging of extremist views being allowed in Labour, or of an individual with no place in a modern political party being granted membership nonetheless.

In recent days, a Labour Party member has accused Israel of being behind the Brussels bombing. An aide to Sadiq Khan, the Labour mayoral candidate in London, was revealed to have glorified rape and homophobia on social media. Another was exposed as having defended the 2011 student riots and attacks on shops and public buildings.

The apparent rise of anti-Semitism in the Labour Party is striking and alarming. Senior figures have spoken out in alarm about what is going on. Lord Levy, Tony Blair’s former fundraiser, has threatened to quit the Party unless it is stamped out. Chris Bryant, the Shadow Leader of the House, took to the newspapers to warn that there is no room for anti-Semitic views in the Labour Party. Even John McDonnell, the Shadow Chancellor, has called for people who express such views to be expelled from the Party.

That in particular is ironic, since it is McDonnell as much as anyone who has fostered the revolution that is taking place in Labour, with the creation of the Militant Tendency-style Momentum movement, and the bringing together in Labour of many of the most extreme groups in British left-wing politics.

It’s clear that the problem is now a serious one for our politics generally. These are not fringe figures. Last week the Labour former Lord Mayor of Bradford was found to have shared anti-Semitic tweets and the Labour Party in Kensington was embroiled in a row over whether it had readmitted a Labour Councillor who had suggested that Israel might be behind 9/11. A member of Labour’s National Executive suggested that Jeremy Corbyn should sit down and have a cup of tea with ISIS terrorists.

Furthermore, the Momentum movement in Labour, which is the focal point for the new revolutionary fervour sweeping the Party, has clear ambitions to purge Labour and install its own people instead of moderate MPs. Amongst many others, in Streatham Chuka Umunna is facing deselection from militant activists, one of whom accused him of not being “politically black”.

We’ve seen some of this before in Britain. Back in the 1980s, when the Militant Tendency was trying to take over Labour, the left-wing newspaper Labour Herald, co-edited by Ken Livingstone, ran an article praising the achievements of North Korea – at a time when vast numbers of people were being killed in purges.

But Militant never succeeded in taking over Labour. Neil Kinnock saw it off.

Today, things look very different. The so-called kinder, gentler politics that the new Labour leadership claim to espouse masks an undercurrent of racism and bigotry – and a new movement which supports political progress through civil disorder and has no place in 21st Century Britain. And they are determined to succeed where Militant failed before. Labour MPs mostly know this is all wrong.

But their inaction makes them accessories to the crime. These people must never be allowed anywhere near Government.