There are two facts about Brexit that everyone seems to forget every few weeks: the first is that Jeremy Corbyn is a Eurosceptic. The second is that the first fact doesn't really matter.

The Labour leader's hostility to the European project is back in the news after he told Andrew Marr that the United Kingdom's membership of the single market was inextricably linked with its EU membership, and added for good measure that the “wholesale importation” of people from Eastern and Central Europe had been used to “destroy” the conditions of workers, particularly in the construction industry.

As George Eaton observes on Twitter, Corbyn voted against the creation of the single market in 1986 (and the Maastricht Treaty, and the Lisbon Treaty, and so on and so on). It would be a bigger shock if the Labour leader weren't advocating for a hard exit from the European Union.

Here's why it doesn't matter: most Labour MPs agree with him. There is not a large number of Labour votes in the House of Commons that would switch from opposing single market membership to supporting it if Corbyn changed his mind. (Perhaps five or so from the frontbenches and the same again on the backbenches.)

There is a way that Corbyn matters: in reassuring Labour MPs defending majorities in heavily pro-Remain areas that things will be OK. Imagine for a moment the reaction among the liberal left if, say, Yvette Cooper or Stephen Kinnock talked about the “wholesale importation” of people or claimed that single market membership and EU membership were one and the same. Labour MPs in big cities and university towns would be a lot more nervous about bleeding votes to the Greens or the Liberal Democrats were they not led by a man who for all his longstanding Euroscepticism appeals to the values of so many Remain voters.

Corbyn matters because he provides electoral insurance against a position that Labour MPs are minded to follow anyway. And that, far more than the Labour leader's view on the Lisbon Treaty, is why securing a parliamentary majority for a soft exit from the European Union is so hard.