What is changing matters politically is not the numbers that Labour and other progressive parties can produce with the Liberal Democrats; it is rather the unwillingness of a strong number of Labour people on the back benches to support such a coalition.
They want to go into opposition, to 'regroup' and find a leader first. Many simply will not support the more attractive electoral change Liberal Democrats want to see. Party discipline in a multi-party set-up will not be as strong, because it would go across tribal loyalties. Also, many Labour MPs do not like the primary thinkers and negotiators being Alistair Campbell and Peter Mandelson, neither of whom have been elected.
Then there is the fact that we don't know who the Labour leader would be. A Prime Minister does not have to be a Labour leader, but how could one be chosen quickly? It is under these conditions that the party that increased its votes and seats could take power, with its leader known ahead, albeit moderated by Liberal Democrat involvement. If someone like Alan Johnson were in power now, the situation would be different.
There is no love lost between Labour and the Nationalists either. That again is a Labour problem that prevents coalition. Under a PR system, even Alternative Vote, Labour would have to learn to behave otherwise.
There is one area where Liberal Democrats and Conservatives apparently have more in common, and that is in the erosion of civil liberties under Labour. But there is no doubt that much will be uncomfortable between the two parties, and could have electoral consequences if the Conservatives prove to act in a way that seriously contradicts how Liberal Democrats voted.
Normally in PR the swings of power go with the mood of the country, and under PR and with this Commons mathematics the Conservatives would assume power. But this has been under first past the post, and so moving to political change justifies a so-called 'coalition of the losers'. It would make up 52% plus of the electorate. The problem is on the Labour side; too many are unwilling, and are saying others can rule while we sort ourselves out, whilst others in Labour fear for peoples jobs and the public services and see holding power as far more important.
As I understand it, there is no chance down the line for a switching of sides, say in two years; in that, constitutionally, a Prime Minister can dissolve parliament when a majority is lost. Someone else might say, "I can command the House of Commons," but it is the Prime Minister who in all effect carries the powers said to be with the monarch. So once Cameron has the keys to Number 10, it is his power to cut and run. Perhaps there will be an agreement that he won't, though it may not be worth the paper it is written on.
The point is that those of us who'd favour a progressive alliance cannot have it if the Labour Party cannot deliver. On that basis the least worst is Liberal Democrat moderated Conservatives. It is much better than Conservatives alone. A free vote throughout the House of Commons, and some whipping among Labour, for AV may be the best the Liberal Democrats can get and probably after Labour has chosen its next leader.