PETER OBORNE: Why January 15 is Britain's most momentous date since the Second ...

Very occasionally — indeed, rarely more than once in a generation — a nation’s whole mood changes. 

The unthinkable becomes thinkable. The impossible becomes possible. The tectonic plates beneath the Earth’s crust begin to creak.

Britain experienced such a moment in May 1940. Prime Minister Neville Chamberlain had lost control of his Conservative Party, opening the way for a deeply distrusted outsider. 

That man was Winston Churchill and, of course, history eventually proved him to be a national hero.

A lesser example occurred in November 1990. Margaret Thatcher had been omnipotent for more than a decade. Yet suddenly, amid deep social divisions caused by the introduction of her poll tax, the Iron Lady became broken, humiliated and left No 10 in tears.

This weekend, again Britain faces a week ahead of monumental importance. It is no exaggeration to say that the outcome of events over Brexit will affect the lives of each and every one of us. Indeed, that is not often said of political decisions.

Forget all the talk of the past 31 months about the 17.4 million who voted to leave the EU and the 16.1 million who said they wanted the UK to remain. What happens over the coming days and weeks will have huge repercussions for every one of Britain’s 66 million people.

At the moment, eyes are on Prime Minister Theresa May. There is a possibility that she will no longer be in No 10 at the end of next week if she loses Tuesday’s Commons vote.

Over the past months, she has clung to office in the face of disloyalty from fellow Tories, abominable treatment by Brussels, irresponsible posturing by rival parties and a series of personal humiliations.

Her stoicism has, in many ways, been admirable. But can she survive if her Brexit deal is rejected by MPs — as seems most likely — on Tuesday? Of course, she could win. I fervently hope she does. If she prevails, the result should be that Britain will leave the EU in relatively good order on March 29.

Mrs May’s political legacy would be secured as the heroine who forced through a version of Brexit in the face of the unforgivable treachery of senior colleagues and against all the odds. Indeed, the BBC has a published forecast — surely very wide of the mark — that the PM could lose by a margin of more than 200 votes.

The biggest defeat suffered by any post-war British government was the 86-vote loss suffered by Labour Prime Minister Jim Callaghan in 1978 over a Scottish Bill.

By the normal rules of politics, Britain would be looking for a new Prime Minister if Mrs May suffers a three-figure defeat. For any government leader unable to get a key policy through Parliament ought by rights to be finished.

But these are not times of normal politics. I believe there is hope for Mrs May if she loses.

Yes, defeat would be devastating. Yes, Mrs May would be humiliated and a husk of a prime minister. She would be in office but not in power — to use the contemptuous phrase levelled against Prime Minister John Major by his sacked Chancellor Norman Lamont 25 years ago.

That said, she could still survive in such extraordinary circumstances. Having seen off a challenge to her leadership from rebel, hard-Brexiteer Tory backbenchers in December, under party rules she cannot face another challenge for 12 months.

Of course, as head of a minority government, she is very vulnerable to a Commons vote of no confidence. Over recent weeks, Labour has huffed and puffed about whether to force such a vote.

My guess is that if there is such a vote, Mrs May would survive. Her mutinous backbenchers, terrified of a General Election, would rally round and she would narrowly win the day.

Even so, she would still be seen as a dead duck PM and be unable to command either her own destiny or that of the nation.

The brutal truth is that whatever happens next week, power is steadily seeping away from Theresa May.

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