Let’s quote her to get the flavour of it.  Anna Soubry says that “my front bench… is in hock to 35 hard ideological Brexiteers who are not Tories.  They are not the Tory party I joined 40 years ago and it is about time Theresa stood up to them and slung ’em out. They have taken down Major, they took down Cameron, two great leaders neither of whom stood up to them.  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. Unless Theresa stands up and sees off these people she is in real danger of losing huge swathes of not just the parliamentary party but the Conservative Party.”

Much of all this presents considerable obstacles to sober thought.  Who are the 35 Tory MPs in question?  Perhaps the Broxtowe MP is referring to the European Research Group, to which some seem to credit the almost supernatural powers that Disraeli ascribed to the secret societies.  But the ERG probably has nearer 80 members than 35.  And it doesn’t vote as a rebellious block in the Commons – or hasn’t yet, at any rate.  Nor is the ERG responsible for Government policy on leaving the Single Market and the Customs Union, of which Soubry is critical.  That was announced in a speech by Theresa May to the Conservative conference of 2016.  She, Nick Timothy and Fiona Hill seem to have taken the decision between them.

It is true that three Tory Prime Ministers were plagued by rebellion and revolt over Britain’s relationship with the EU – Cameron, Major and Margaret Thatcher, who the Broxtowe MP doesn’t mention.  But only one of these was “taken down” by Conservative MPs: the last.  Cameron resigned after losing the EU referendum.  (More than 80 pro-Brexit MPs signed a letter asking him to stay on if Britain voted Leave.)   Major quit after the Blair landslide of 1997.  Thatcher alone was forced out by a leadership challenge.

But it is probably a mistake to parse the Broxtowe MP’s cri de couer in this way.  It was powered not so much by careful thought as by seething emotion.  The Conservative Party has changed since the late 1970s, when it was more Heathite than Thatcherite.  It was pro-EU membership; now it is anti, in the referendum’s wake.  She doesn’t like the change.  She has every right not to.  But when she says that Boris Johnson and Jacob Rees-Mogg are “not proper Conservatives”, she moves beyond expressing her feelings to making a claim – and, unwittingly, doing us all a favour.

Which is to remind Tory and non-Tory alike how difficult it is to define what conservatism is.  Socialism is an international creed.  Conservatism has a more local flavour.  In France, it can favour protectionism and an interventionist state.  In America, it has a more pro-market bias than here.  In Ireland, it isn’t formally organised at all – though the grandfather of conservatism was an Irishman, Edmund Burke.  And so on throughout Europe and the Anglosphere.

Some say that the core of conservatism is a belief in freedom.  It depends what you mean.  If by freedom, one means the right of the individual to do whatever he wants if others aren’t harmed, that’s a view whose origins lie in liberalism.  If one means instead the nexus of Britain’s institutions, the rule of law, a free economy and strong civic institutions, then that is nearer the mark.  But there is room for doubt.  Keith Joseph spoke of the social market economy.  The Conservative Party has been for protection, not free trade, for long periods of its history.  Not all modern Conservatives have the Tory reverence for institutions.  The Party and its supporters have no monopoly on reverence for the rule of law.  Others trumpet aspiration.  Others still, social justice.

And others that conservatism is inextricably linked to self-government – and, smashing Soubry’s serve back over the net, will say that she isn’t a proper Conservative.  But where is it written in tablets of stone that Conservatives must be Brexiteers?  Cameron, Michael Howard (when Party leader), Iain Duncan Smith (ditto), William Hague, John Major, Margaret Thatcher (as Prime Minister) – none of these, at the time, were for Leave.  Admittedly, conservatism and the Conservative Party aren’t identical.  But it would be odd to say that they aren’t linked in some persistent way.  Our take is that the essence of conservatism in Britain has something to do with a distrust of utopian schemes, an attachment to our institutions, and the belief that people will take better decisions for themselves than the state.

However, your view is as good as ours.  Or Soubry’s.  She has no more or less right to decide what a proper Conservative is than you or this site or anyone else.  That said, her words suggest one of the oldest definitions of all – namely, that someone who isn’t a proper Conservative is a conservative with whose conservatism one disagrees.