May's tenure - however disastrous - has taught us one lesson worth learning

The Speaker has rebuked the Government for being “discourteous”. To wait until the last possible moment to announce an indefinite delay in holding the “meaningful vote” on the Withdrawal Agreement does indeed look chaotic. But does courtesy come into it? All governments act in their own interest as well as — we must hope — the national one. It was only when Theresa May felt she had no alternative that she blinked. It was hardly a matter of courtesy, but rather of survival.

And yet courtesy matters in politics as much as anywhere else. The Labour MP who seized the mace, Lloyd Russell-Moyle, was stopped by two Serjeants-at-Arms and then “named” by the Speaker, who ordered him to withdraw for the rest of the sitting. He deserves condign punishment, if only pour encourager les autres.

One trusts that the voters of Brighton Kemptown will not forget their Member’s insult to the symbol of parliamentary democracy. Michael Heseltine got away with similar behaviour in 1976, but Mrs Thatcher demoted him in the Shadow Cabinet and thereafter his reputation for bad manners helped to deny him the premiership that he considered his due. There have always been rare incidents of rash and improper conduct on the floor of the House, which is why the two front benches are kept two sword-lengths apart. But actual assaults are few and unparliamentary language severely sanctioned.

More importantly, the circumstances in which prime ministers are expected to resign are governed by convention rather than strict rules. In our “removal van democracy”, the loss of a majority in a general election normally obliges the incumbent to leave Downing Street forthwith. But it is not unusual for prime ministers to step down in between elections on points of principle or even honour.

Some of our greatest statesmen have resigned rather than continue in office after their most cherished legislation was rejected by the Commons. Examples include Sir Robert Peel, who resigned in 1846 on the principle of free trade, and W.E. Gladstone, who resigned twice in 1886 and 1894 on the issue of Irish Home Rule.

Others have resigned because they felt power slipping away and wanted to preserve party unity: Chamberlain resigned as Prime Minister but not as party leader after the Norway debate in May 1940 to make way for Churchill; Margaret Thatcher resigned in 1990 rather than fight a second round of a deeply divisive leadership contest; and Tony Blair reluctantly made way for Gordon Brown in 2007 rather than risk a coup that would have destroyed the Labour government.

Another group have “retired” on grounds of age or health: they include Salisbury, Ramsay MacDonald, Baldwin, Churchill, Eden, Macmillan and Wilson. Most of these lived a long time after leaving office, so their resignations must be seen as gestures of courtesy too, saving their colleagues the indignity of removal by force. The last sitting Prime Minister actually to die in office was Campbell-Bannerman, though Labour have lost two Leaders of the Opposition who would almost certainly have entered Downing Street had they lived: Hugh Gaitskell and John Smith.

So what do all these precedents mean for Theresa May? She must know that her days in office have been numbered since her disastrous election last year. But she wishes to be remembered as the Prime Minister who delivered a version of Brexit that healed the wounds inflicted by decades of division and discontent over Europe. So in her short time in Downing Street she has already acquired a reputation for clinging to office.

That reputation is as yet unjustified. Mrs May has every right to give the deal she has negotiated over two years her best shot. But if and when the House of Commons rejects it decisively, it will be time for her to make way for another leader who can honour the referendum result and reunite the nation. The Prime Minister knows this, even if she cannot say so in public.

Was the decision to postpone the meaningful vote motivated by nothing more than Mrs May’s desire to stay on until the New Year? That is hard to believe. More likely, she hopes against hope that her EU counterparts will offer her a lifeline, perhaps in the shape of the elusive get-out mechanism for the Irish backstop. But they have already ruled this out. Just in case the whole agreement were reopened, the vultures are circling in the shape of Spanish designs on Gibraltar, French demands for fishing rights and many other encroachments on British sovereignty.

So the logic of the situation points towards a prime ministerial resignation, and sooner rather than later. Mrs May has spent almost all her political capital and politics is an unforgiving profession. But even if her successor ends up delivering a “managed no deal Brexit”, the May era will not have been in vain. It will have proved that the attempt to negotiate with an implacable European Union was doomed to failure. If Mrs May had left without a deal two years ago, as many Brexiteers now insist that she should have done, then Remainers would always have claimed that better terms would have been on offer. We now know that Brussels was never going to be generous — but only with hindsight.