oris Johnson has built his Brexit negotiation on the two people who were furthest apart: Leo Varadkar, the Irish prime minister, and Arlene Foster , the leader of the Democratic Unionist Party.

Unexpectedly, in face-to-face talks in Merseyside last week, Johnson and Varadkar agreed “they could see a pathway to a possible deal”. In the negotiations that followed, Johnson kept Foster informed every step of the way.

That is because, while Varadkar is the key to an agreement with the EU, Foster is the key to securing a majority in the House of Commons for a deal. There are only 10 DUP MPs, but such is the balance of forces in this hung parliament that theirs are the critical swing votes.