To understand the gang of seven’s chance of success it’s important to get the history rightby Matt Singh / February 20, 2019 / Leave a comment
This week’s move by seven Labour MPs to quit the party will no doubt evoke memories of the Labour-SDP split in 1981 which, it has often been claimed, gifted Margaret Thatcher her landslide at the next general election.
The rationale for this theory is intuitive, since the gang of four, and every subsequent defector bar one came from Labour. Moreover, the changes in the popular vote between 1979 and 1983 look a lot like they would if the only major move were a split on the left. The Conservatives lost 1.4 points, Labour lost 9.4, and the Liberal-SDP Alliance gained 11.9 points. And the national pattern was repeated in seat after seat.
This is, however, a gross oversimplification. Changes in popular vote share are the sum of a number of offsetting flows of voters in different directions. And even if we knew these flows, we still don’t know for sure how people would have voted without the SDP’s intervention. It’s often assumed that absent the split (and the Alliance surge), 1979 Labour voters would simply have stayed loyal.
Ivor Crewe and Tony King examined this in their 1996 book SDP: The Birth, Life, and Death of the Social Democratic Party, and found it wanting. Though because data they were using required them to extrapolate from the imputed second preferences of a small subset of Alliance voters, their findings are necessarily accompanied by a bit of an asterisk.
We do, however, have an alternative data source. The 1983 British Election Study asked how people had voted in that year’s election, as well as in 1979. But the BES also asked people what their second choice of party would have been.
The relevant group here is the five million people who didn’t vote for the Liberals in 1979, but did vote for the Alliance in 1983. This group did back Labour more than the Conservatives in the previous election (though not exclusively).
How might these Alliance switchers have voted in the absence of the SDP or resurgent Liberals? The BES second preferences suggest that roughly as many of them would have voted Tory (50 per cent) in 1983 as Labour (45 per cent).
If we assume that the Liberal vote had remained at 14.1 per cent and reallocate the 11.9 point Alliance…