I'm not sure if the Labour party is falling apart or not. It is certainly needed to now put up an opposition, along with the SNP, and it needs maximum discipline on attendance to exploit indiscipline in the Conservative Party among its usual subjects and a few others.
If we are going to be part of the EU then we need free movement of labour along with free movement of capital: this is not just capitalism but because there is a humanism involved in the free movement of people within the continent, and it slowly dissolves the ethnic nationalisms that are behind the immigration debates.
Note that Scotland's civic nationalism has avoided the immigration problem, as indeed the SNP remains pro-European. The peacefulness of last year's referendum was a beacon to the world.
Scotland has multiple historic ethnicities as well newer ones, and has had its own clashes of culture in the past - Jacobite versus modernist, Anglicised gentry versus old clans, urban collective Labour and rural communities, its own far north tending to Scandinavian. The Scottish contribution to the UK was somewhat homogenised in recent decades, by gentry and by unions, and its distinctiveness now is more historically attuned.
On this basis, the Labour conundrum of more left wing north and less left wing south may only be solved (minimally, sufficiently?) by having Scottish Labour go independent.
Labour will make a great mistake if it goes in favour of having an EU referendum. Let the Tories have this and tie themselves in knots.
Cameron has to do a sham negotiation. If he claims he's satisfied (the EU Council of Ministers throws him a few bones) the Tory nutjobs will go bananas. The Tory party will have to be split during a campaign. If Cameron is dissatisfied and says so a minority of the Tory party will not want to leave the EU, and a vote to stay in is still likely. Cameron may be dissatisfied and still say we ought to stay in - nutjobs alert again. He might recommend coming out gambling on staying in - but would he be able to stay as Prime Minister? To come out will have a major effect on business and industry, the massive reverberations having unknown effects.
A vote to stay in the EU would tear the Tory party apart, simply because the nutjobs will have lost their long awaited vote. There will be talk of treachery and more.
The effect of the EU referendum politically could be worse than Lamont and Cameron's ERM crisis, when interest rates shot up to hold the pound's value and then we were forced out. Major's government never recovered, with the icing of the nutjobs ("bastards") and sleeze on the cake.
Forget about the Fixed Term Parliament Act and the majorities needed to have an election. It just needs repealing by a simple majority. Then it depends on who can call an election: maybe then a simple majority of the House of Commons.
This government will be crippled by the device it has used to keep the Tory Party together under Cameron's leadership. The 70 plus majority that the Liberal Democrats provided is no longer available for its self-interested policies.
This is why one can expect scorched earth from the Tory government starting with the July budget. They'll have two years and then deep trouble. Let the Tories stew in their own juice.