The resignation of David Davis is a devastating blow to Theresa May’s authority. After the Chequers summit on Friday, her supporters loudly boasted of her achievement in imposing unity on the Cabinet with her phantom Brexit strategy. That complacent triumphalism has now been blown apart.

Badly weakened, the Prime Minister may survive Davis’s departure. But her immediate prospects would be much grimmer if her Foreign Secretary Boris Johnson were to quit today. To lose one senior pro-Leave Cabinet Minister might be a misfortune. To lose a second one in the space of 24 hours could be fatal.

That is precisely why Boris should go. A terminal crisis for May is what the Government and the Tory Party need. Her dismal, chaotic farce of a premiership should be brought to an end, otherwise any hopes of a meaningful Brexit or a Conservative revival are doomed. Her two years of stumbling and sloganising in Downing Street have only managed to weaken her Government, destroy her Parliamentary majority and squander the opportunity to embrace British freedom.

By his resignation today, Boris could bring about a fresh start for the Conservatives and Brexit. This is the moment to strike. If he fails to act, despite all the humiliation heaped on him by the Downing Street machine, then he will lose all credibility. But if he departs in protest at the Chequers proposal, then he will be doing a huge favour, not only for British democracy, but also for his own career.