The Conservatives still have the power to keep extremists out of the party – for now

This is the moment of maximum danger, when officials need to be vigilant about what is happening to the wider party

The Conservatives can resist this insurgency – but if the leadership and the machinery falls to the likes of Boris Johnson, it will be ‘game over’ (AP)

Conservative members of parliament, and indeed officials and ordinary party members, are worried about entryism. So concerned, indeed, that they have popped across the political aisle to approach Labour advisers from the Blair-Brown era. They would like to know what to do about the influx, the kind of phenomenon that has plagued the Labour movement almost since its inception, but has hitherto been unknown on the right.

The obvious advantage that the Conservatives possess for the time being is that the extremists have not yet taken over the leadership. That is the important contrast with the current state of the Labour Party, under Jeremy Corbyn. For as long as Theresa May and her appointed apparatchiks control the machinery, they can control who becomes a member.

Although the Conservative associations are still semi-autonomous, they do not enjoy the complete freedom of action they did before the Victorian National Union structure was reformed under William Hague’s leadership. The Conservative “rule book”, including the mechanism for making policy and selecting a leader, could usefully be amended to make the party safer for its true traditions and democracy. Had Ed Miliband done that when he had the chance – and not foolishly opening his party membership to all comers – Labour might not be in quite the predicament it finds itself today. One wonders what unpredictable effects Sir Vince Cable’s similar move might have on the Liberal Democrats’ complexion.

It is not a human right to be a member of any particular political grouping. Parties have a say in the matter too. Ukip, whence so many of these guerrillas come, has quite a few rules about former membership of the British National Party, for example.

Currently Ukip, “led” by Gerard Batten, is so hopeless that it is being forsaken by the likes of Banks and Farage, and is desperately courting strange new friends. It is thinking aloud about allowing Tommy Robinson, of the English Defence League, to acquire a membership card. Regrettable, but that is a matter for the party. It is also a matter for the Tories as to who they allow in.

Many of those now seeking to join or rejoin Conservative associations dedicated their recent political efforts, and much money, to destroying the Conservatives’ chances of forming a government. David Cameron called them, memorably, “a bunch of fruitcakes, loonies and closet racists”. All that is disqualification enough. Former Ukip members should be subjected to especial scrutiny.

Tory entryism – “Blue Momentum” – is, some say, an odd concern, given that the party is about a quarter of the size it was in the years when it formed part of the weft and weave of national life, in towns, cities and the countryside alike. “Normal”. In the 1950s, “normal”, apolitical people were Conservative members, and the Young Conservatives were a million-strong club that served principally as a marriage bureau for the upwardly mobile, the Tinder of its day. It has been downhill ever since.

The Tory grassroots’ usual problem, it has often been observed, is that there are too few of them, and they tend to be old, thus unrepresentative of the society they seek to inspire. They are more extreme than either Conservative voters or MPs and, to borrow a phrase used by Ms May when she was party chair, look nasty as well.

The problem is that it would serve the party ill for them to become still more extreme. The self-styled “Bad Boys of Brexit” are seeking to turn the Conservative Party into a vehicle for hard Brexit and Boris Johnson’s leadership ambitions. They make little secret of it. Inspired by Labour’s influx of members from the Momentum movement, and the subsequent definitive lurch to the left under Mr Corbyn, they hope for a mirror-image success on the right. After three months, they will be eligible to vote for a replacement for Theresa May, not to mention agitating for more extreme policies across every sphere of political life, but especially on Brexit.

The threat to the Tory establishment is real. Ex-Ukip figures such as Arron Banks and Andy Wigmore say that they were once fully paid-up members of the Thatcher-era Conservative Party, and in any case the party’s policy is to leave the EU. That is what they campaigned for in the Leave.EU group, the more freewheeling end of the Leave campaign that was dominated by Vote Leave and its Conservative cabinet minister figureheads. They protest, sometimes a little disingenuously, when Conservative central office rejects their applications.

Yet CCO is right to do so, and needs to hold the line. This is the moment of maximum danger, when officials need to be vigilant about what is happening to the wider party. It is in nobody’s interests for the Conservative Party to be captured by a truly entryist gang. Here there is a further contrast with Labour today.

Labour’s Momentum is, for all its faults, a genuinely mass membership group, and unlike the classic Trotskyist cells such as Militant, which took over moribund local parties and union branches in the 1970s and 1980s. Militant, a tiny “pestilence” as it was called, used Labour’s rickety pyramidal power structure to capture the wider party machinery in a grossly undemocratic fashion. That is really what this new band of hard-right Leavers represents, and it stands equally able to capture similarly somnolent Conservative structures. A few committed ex-Ukip hardliners can capture a constituency and deselect a sitting Tory MP.

Mercifully, the Conservatives have never been as fetishist about a “sovereign” party conference, nor as democratically minded. Much power resides with the parliamentarians, where common sense resides, outside the rump of the 80 hard Brexiteers of the European Research Group. CCO can vet prospective members. The Conservatives, in other words, can resist this insurgency – but only for as long as the moderates retain the leadership and the machinery. Once that falls, to Boris Johnson, say, or Jacob Rees-Mogg, or, nightmarishly, Nigel Farage, then it will be “game over” for the Tories.

The Brexit revolutionaries that Mr Cameron surrendered to, and Ms May afterwards tried to appease in order to save the Tory party, will end up consuming it. There is little satisfaction to be derived from the gruesome spectacle.