The last major split in a UK party was the event that ended up creating the LibDems - when the Gang of Four left Labour to found the SDP.
Three of the four were substantial political figures: Roy Jenkins had been Chancellor, Home Secretary and President of the European Commission; Shirley Williams had been Education Secretary and mounted a credible challenge for Labour's Deputy Leadership; David Owen had been Foreign Secretary. But Williams and Jenkins were both out of Parliament. Without Owen, there would been no SDP. Jenkins and Williams would probably have joined the Liberal Party, with or without the deeply insignificant Bill Rodgers. Owen was thus critical in creating the LibDems, a party he refused to join. Without him there would only have been a slightly larger Liberal Party.
Equally significant was a man who not only never joined the LibDems but refused to join the SDP either: Roy Hattersley. If he had joined the SDP they might indeed have 'broken the mould' and ended up supplanting Labour as the main opposition party.
Hattersley was, and remains, deeply, tribally, Labour. He hated the way his party was going in the 80s, and for different reasons again now. Yet, there was a point when he held the future of the Labour Party in his hands, and decided that Labour should live. If Hattersley had joined the SDP at its founding it is fair to assume that several other MPs who struggled with their conscience and unltimately decided to stick with Labour would have done the same. Certainly some of those who hesitated, and ultimately defected later, would have abandoned ship in early 1981 instead of at the year's close.
This is significant, because that tranche of late defectors gave Denis Healey his majority in the 1981 Deputy Leadership election. Without them, Tony Benn would have won, and prompted a second wave of defectors. Some 20 MPs defected from Labour to the SDP. If Hattersley had jumped and Benn had triumphed over Healey, the total would have been at least double that.
Leap forward to 1983. A party led by Michael Foot and Tony Benn would have looked totally different to one led by Michaelf Foot and Denis Healey. By a small margin Labour held on to second place, and Benn called it the largest ever vote for socialism. In this parallel world, the Alliance would have surpassed Labour in the popular vote, though probably not in terms of seats won.
Third place, and the defeat in the general election of the Party's Deputy Leader, (Benn lost his Bristol seat that year) would have left the Party in chaos. Kinnock might still have won the leadership of the rump party, but without his dream ticket ally. Michael Meacher would have become his Deputy. Third place would have prompted a third wave of defections, probably including the new MP for Sedgefield, Tony Blair.
So what happens if the LibDems split this year? Who will lead the defectors to the Conservatives? And who will stay behind to play the Hattersley role?
Certainly, the significant names in play are David Laws and Nick Clegg. Laws is one of the brightest Orange Book liberals. It is said he only joined the LibDems rather than the Conservatives because of his social liberalism, a strand now dominant in the Conservative Party. Nick Clegg is widely considered a future leader, as David Owen once was in the Labour Party.
If both of these defect, perhaps Chris Huhne will take the Hattersley role. Perhaps it will be left to Ming Campbell to hold the Party together, and perhaps he will fail.