Of course Theresa May should sack Boris Johnson – but that won’t solve this government’s problems

Boris Johnson’s survival as a cabinet minister is a living rebuke to the prime minister. His colourful language has caused the government continuous problems over leaving the European Union.

His public challenge to Theresa May last week to avoid a “bog roll Brexit, soft, yielding and seemingly infinitely long”, was unhelpful enough; more incendiary was his private, jocular and coarse dismissal of business concerns about Brexit. He won his place in cabinet as the leader of the Leave campaign in the referendum, and yet has contributed worse than nothing to the slow development of the government’s negotiating position.

It is not as if he has such an outstanding record in his day job as foreign secretary that Ms May should hesitate to sack him. The Independent sought to be fair to Mr Johnson when he made an honest mistake about Nazanin Zaghari-Ratcliffe, the British-Iranian detained in Iran, and to give him credit for visiting Tehran in an attempt to remedy the damage. But he has achieved nothing of note in nearly two years in office, except to make British diplomacy look trivial and foolish.

Nor has Mr Johnson emerged from last night’s House of Commons debate on Heathrow with his reputation enhanced. Having promised his constituents in the usual colourful terms that he would “lie down in front of those bulldozers” to prevent a third runway being built, he took the coward’s way out and flew to Afghanistan to avoid the vote.

It is true that, as he is reported to have said, his resignation would not have changed the vote, a huge majority of 296 in favour. Indeed, almost the only argument for keeping Mr Johnson in office is that The Independent shares his doubts about Heathrow on environmental grounds. But trust in politics depends on politicians keeping the promises they make – or at least explaining why they have changed their minds.

Talk of Mr Johnson’s departure from ministerial office, even if it comes from him, reminds us that Ms May’s problems of cabinet discipline go rather wider than the Foreign Office.

David Davis, the Brexit secretary, has forced the prime minister to change course twice this month by threatening to resign, first on the draft of the “temporary customs arrangement” and then on the terms of the deal to buy off Dominic Grieve’s rebellion on the EU (Withdrawal) Bill.

And the success of Jeremy Hunt, the health and social care secretary, in securing an austerity-busting five-year deal from the Treasury, with Ms May’s support, has emboldened other spending ministers into making their pitches.

The most inept demand has come from Gavin Williamson, the defence secretary, who wants a large sum to underwrite the suddenly vogue phrase, “tier 1” status. Mr Williamson is right, as we report today, that the defence budget is approaching one of those periodic moments when a choice must be made to drop ambitious programmes or to spend more. But this is not a question that should be settled by macho posturing or veiled threats to bring the prime minister down.

Theresa May has been in a weak position since she lost her parliamentary majority last year, but the recent disintegration of cabinet unity is getting in the way of good government – and making it less and less likely that it will be capable of negotiating a good Brexit deal.