David Cameron's mighty gamble is based on a number of unknowns and what ifs. The age of uncertainty has begun.
The Prime Minister believes, if he is returned to power in 2015 with a majority government, he will need only two years to persuade our European partners to accede to a future Conservative government's wish list on repatriating powers.
And, intriguingly, he failed to answer what would happen if they refused, leaving open the possibility he could lead the campaign to get Britain out.
While German Chancellor Angela Merkel summoned up her best diplomatic response, saying she was willing to discuss Britain's wishes, some of her continental colleagues were not so co-operative.
Laurent Fabius, the French Foreign Minister, insisted the UK could not seek an a la carte EU menu but must, like everyone else, stick to the set one, while Guy Verhofstadt, the former Belgian premier, accused Mr Cameron of playing with fire.
The people of Scotland, facing a referendum on Scotland's place in the UK next year, will, if they say no, face another one three years down the line on the UK's place in Europe. And if they say yes in 2014, there is the possibility that while the Government at Holyrood is trying to get an independent Scotland into the European Union, the Government at Westminster will be trying to get what remains of the UK out.
Alternatively, it could be Mr Cameron succeeds and gets the reformed Europe he seeks with a "reset" UK relationship, where powers are repatriated. He could end up with a much better deal for the UK than Alex Salmond can get as head of the government of a newly independent Scotland.
Certainly, in the short-term, the SNP leader and his colleagues believe the Prime Minister is playing into their hands on Europe. The First Minister insisted it was now the "persistent undercurrent of Tory Euroscepticism" which posed the biggest threat to Scotland's position in the EU; in other words, if Scots want Scotland to stay in Europe vote yes in next year's referendum.
The Nationalists even insisted the Conservatives were now the true separatists.
It was interesting to note how some of the passages Mr Cameron used on issues like democratic consent could easily have been uttered by Mr Salmond about Scotland's relationship with the UK.
In the Commons, the SNP's Mike Weir pointed out the UK Government had condemned the Scottish Government for spending two years on holding the independence referendum – citing time and again the wait was causing uncertainty for jobs and investment – yet the Tory-led administration was proposing a "five-year marathon" until the EU referendum. Mr Cameron gave a garbled response, which did not answer the point.
In the heat of PMQs, Ed Miliband insisted Labour was completely against an in-out referendum as the uncertainty would not help jobs and growth, which, he insisted, was the country's priority.
Later, the Labour leader's apparently blanket "no" was nuanced, with aides suggesting no-one could know what the future held.
This general position is shared by Nick Clegg and the Liberal Democrats, which means the issue of Europe has opened up yet another deep fissure in the Coalition.