It was former prime minister Harold Wilson who coined the phrase "a week is a long time in politics" to try to capture the fast-changing, momentous shifts in fortunes for a politician or a political group in the course of a single week.

And it's a quip that encapsulates what lies before our politicians, parliament, government and country as we enter a truly momentous week which could realign British politics along Brexit divisions, reshape who governs us and how our economy is run.

It could change not just our relationship with Europe but the contours of our Union too.

Because what happens in the next 72 hours will decide whether we'll have a Brexit general election which will transform our political landscape as the government and parliament square up over Brexit.

MPs will move to take control of Commons' business and pass an emergency bill to block a no-deal exit on 31 October and if they succeed the prime minister has made clear he will have no option but to try to hold a snap election.


Mr Johnson will frame it as a poll foisted upon him by parliament as he seeks to rally his Vote Leave base once more in the form of a "people versus parliament" general election.

Number 10 has pencilled the election in for 14 October - three weeks before Brexit day and on the eve of a crunch European Council summit. I can just imagine the slogan: Back Boris to deliver Brexit.

An election run on Brexit lines rather than traditional party ones, it will settle too the decades-old Conservative civil war on Europe: those unwilling to back Brexit at any cost will be purged from the party. Those who served in cabinets under David Cameron and Theresa May will have the whip withdrawn if they rebel against Mr Johnson to block no deal.

Former chancellor Philip Hammond, who was just a few weeks ago the second most powerful cabinet member, could be facing the end of his career as a Conservative MP as No 10 tries to bar him from standing as Tory candidate in any election (although his local association did re-select him on Monday night).

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And this rebel will be joined by up to two dozen fellow travellers - including former cabinet ministers David Gauke, Rory Stewart and Greg Clarke and the father of the house Ken Clarke - as the pro-European, liberal wing of the Conservative party is in effect cauterised.

Whether it happens or not rests on critical votes on Tuesday and Wednesday. On Tuesday MPs will try to seize control of the order paper so they can then push through a private members bill on Wednesday to prevent the UK leaving with no deal on 31 October.

Tuesday's vote will be crucial because if MPs succeed in taking control of Commons business, they will be confident that the numbers are there to force through an emergency bill to block a no-deal exit on 31 October.

The government at this point will then press for a vote to hold a general election. That could come on Wednesday or Thursday. It can only happen if two thirds of MPs vote to dissolve parliament and have an election.

Again, there is no definitive answer on whether that vote would pass. The Labour Party have consistently said they want a general election but they are also watching hour by hour to see how this situation evolves.

I'm told the Labour leadership is seeking assurances that any election would be no-deal Brexit proof amid fears that Mr Johnson might play dirty tricks and call an election on 14 October only to then use executive powers and shift it beyond 31 October.

Indeed, Tony Lloyd, shadow Northern Ireland Secretary and a senior ally of Jeremy Corbyn, said last night Labour was not going to support a snap election plan if it means risking quitting with no deal. "Will we fall for Boris Johnson's trick, no we won't," Mr Lloyd told Newsnight. "Boris Johnson is a man who has got form for reneging on his promises."

As to who will prevail this week, it is simply too close to call. The rebel alliance tells me that the Conservative numbers are holding up well and says Mr Johnson's ultimatum on the steps of Downing Street did little to shift the dial. "I see no sign of colleagues bending," said one rebel on Monday night. "In essence the PM told us what we already knew."

What they are less sure about is whether Mr Corbyn can deliver the Labour votes amid speculation that some MPs in very pro-leave seats might fold for fear of voters' retribution in a snap poll.

Number 10 too are unsure whether they will hold off the rebellion, but are ready to throw the dice. "Of course this is a confidence issue," said one source. "We're being pushing into a cul-de-sac with no options."

Mr Johnson and his team believe that without the no-deal option they cannot hope to secure a deal. And this prime minister's out-by-Halloween red line has been drawn in his own blood. He would rather go down fighting in a general election than renege on that pledge.

Those are the stakes, but I cannot tell you how the cards will fall. By the end of this week, Mr Johnson may be ploughing on with his Brexit negotiations and plans for a no-deal exit after seeing off the rebels - for now.

We could be ending the week firing the starting gun on a Brexit general election in which Mr Johnson re-casts the Tory party as his Vote Leave vehicle prepares to deliver Brexit whatever it takes. Or we could end up in stalemate still should MPs decide to both block no deal and block Mr Johnson's election too.

How this Brexit endgame plays out is as unpredictable as it is momentous.