In the view of the postwar Labour prime minister Clement Attlee, “No government can be successful which cannot keep its secrets.” By that yardstick, still the traditional one in British politics, Theresa May’s government is one of the least successful in our history. This is not merely the view of its opponents. It is also the view of its own key members. Less than a month ago the Conservative chief whip, Julian Smith, admitted to the BBC that “discipline is not as good as it should be”. Brexit, he continued, had generated “the worst example of ill-discipline in cabinet in British political history”.

That’s quite a claim. But it is hard to blame Brexit directly for the extraordinarily reckless new act of indiscipline that took place this week. On Tuesday the government’s national security council, which is chaired by the prime minister and contains senior ministers as well as security officials, agreed that the Chinese telecoms giant Huawei could build parts of the UK’s 5G network. This would normally have been a tightly guarded and unpublicised decision – Attlee, for instance, involved only a few trusted ministers in his momentous 1947 decision to build an independent British nuclear weapon. Instead, the Huawei decision was reported in full detail in the following morning’s Daily Telegraph, which named five cabinet ministers who opposed it, and laid the decision directly at the feet of Mrs May.

This leak defied two of the most fundamental – and sometimes controversial – rules of British government: collective responsibility and official secrecy. If a Labour government had leaked in this way, Tory MPs and Tory newspapers would be unable to contain their outrage. Instead, the first reaction of many Tories was to attack Mrs May again. In the excitement, the leak itself was largely forgotten. Nevertheless, an inquiry is now under way. The culture secretary told MPs that he could not rule out a criminal investigation. That could eventually mean a cabinet minister standing trial under the Official Secrets Act.

For good and ill, national security involves – and must involve – secrecy. No ministerial responsibility is normally treated with more reverence than national security. Ministers of all parties regularly intone the sacred responsibility of government to protect its citizens. No government committee has a more august role in this culture than the national security council. When ministers or officials on the NSC unilaterally supply the details of its decisions to the press, something has gone very rotten in government.

This leak exposes the shocking extent to which Mrs May’s government and her party have lost their political bearings as a result of their Brexit debacle. Many ministers seem to have returned to Westminster this week blinded by the ambition to succeed Mrs May – one of them may well have been the source of the leak. Much of the Tory party returned with only one idea on its mind – a leadership challenge which would solve nothing whatsoever about Brexit and could easily trigger a general election in which the Tories could be massacred.

It is said that those whom the gods wish to destroy they first make mad. This seems to be true of the modern Conservative party. Driven crazy by the failure of Brexit and obsessed with the stupid fantasy that a more doctrinaire leader than Mrs May would be more successful than she is, much of the Tory party today displays all the dignity and judgment of a headless chicken, while attracting none of the sympathy. The Tory party used to pride itself on being the natural party of government. Today it is proving itself unfit for government at all.