The Prime Minister's announcement on Brexit, or the lack of it, comes after her de facto Deputy had this morning blithely described the Conservatives as "the party of the Centre". Whatever the opinions of others, that is how it sees itself, a view that it regards as self-evident.
After the First World War, Toryism was redefined by means of one of the great acts of triangulation. In its own mind, it placed itself both between and above two opposite extremes.
One extreme was seen as being Liberalism: individualistic, meritocratic (although the word had not yet been coined), bourgeois, commercial, American. The other extreme was seen as being Socialism: collectivist, egalitarian, proletarian, industrial, Soviet.
To be any of those things very much or, in several cases, at all was to be an extremist, and defined by an ideology in the eyes of people who prided themselves on having none.
There is a reason why you can be talking for half an hour or more to a person who claims to be "not political", only to find out as an aside that you are conversing with the Conservative Leader of the Council, or the Chairman of the local Conservative Association, or someone like that.
You will never, ever have that experience with a comparable Labour figure. No one ever says, "I'm not political, I'm Labour." But the people in question would consider it the most obvious and natural thing in the world to say in absolute seriousness, "I'm not political, I'm a Tory."
In fact, any English organisation, at least, that goes to the trouble of specifying that it is non-political is invariably full of Conservative supporters and even activists.
But the likes of the European Research Group are very political indeed. They are indeed defined by an ideology. Therefore, it is held, they are extremists. And therefore, it is held, they are not Tories.
To someone like Theresa May or David Lidington, that is axiomatic to what would, in normal circumstances, be the point of banality. These, however, are not normal circumstances. So they have had to act. And they have acted.