The chaos of Brexit has provided a number of political shocks which have seen parliamentary institutions lose their credibility with the voters. Yet none have been quite as dramatic as tonight’s sacking from the cabinet by the prime minister of defence secretary Gavin Williamson. An investigation had found “compelling evidence” that Mr Williamson was behind the leak of a controversial decision taken at the government’s National Security Council, which is chaired by the prime minister and contains senior ministers as well as security officials, that agreed the Chinese telecoms giant Huawei could build parts of the UK’s 5G network. Mr Williamson has denied being the source of the Huawei story. Theresa May, who has seen her own authority drain away in the last few months, had no option but to fire a minister who she could not trust with her government’s most sensitive decisions.

The affair raises important questions about the nature and character of politics. There is a strong case for public interest leaking. There may be decisions taken that are immoral or illegal. These the public ought to know about. Others might use the media to get a policy changed as a matter of course. Or in other circumstances a secret may need to be revealed in order for parliament to make an informed decision. All these are reasonable defences of the right to leak. But Mr Williamson appears to have undertaken this act with political goals in mind, namely out of a desire to embarrass cabinet rivals. He has form. In February, Mr Williamson’s threat to deploy a warship in the Pacific forced the chancellor, Philip Hammond, to cancel a trip to Beijing. It is obvious that the premature or anonymous disclosure of information can damage trust and morale within government; but it is also an acknowledged lubricant of political life. No government has appeared able or willing to stamp out this practice. But Mr Williamson’s transgression was of a different order. When a minister, presumably blinded by the ambition to succeed Mrs May, supplies the details of national security decisions to the press, something has gone very wrong in government.

If the former defence secretary had a principled objection to the decision taken by the NSC, he ought to have followed the example set by another defence secretary, Michael Heseltine, who walked out of the cabinet in 1986 in a row with Prime Minister Margaret Thatcher over whether European or American companies ought to rescue a British helicopter firm. Yet Mr Williamson is no Hezza, who was a substantial figure in Conservative politics. By comparison, Mr Williamson comes across as a buffoon. Nowhere was this more obvious than the world stage; telling Russia to “go away and shut up” in the wake of the Salisbury poisoning was rightly ridiculed.

It is symptomatic of the malaise of Brexit that personal ambitions have taken over as the animating impulse in too many cabinet ministers. There appears no depth to which Mr Williamson wouldn’t drop to prove that he had metamorphosised into a nationalist rabble-rouser. He was shallow: responding to Treasury cheese-paring with the idea of mounting guns on tractors as makeshift mobile missile launchers. He showboated: suggesting that Gibraltarians could be armed with paintball guns to fire at passing Spanish ships to scare them off. In response, it was reported, generals simply rolled their eyes. Perhaps nobody else has behaved quite so badly. But this sorry episode reminds the nation that many Conservatives are losing their grip on reality when they ought to be grappling with the most complex piece of statecraft in a generation.