A LibDem-Tory deal to put David Cameron into Downing Street would risk alienating four in ten Liberal Democrat voters who think of themselves and the party as on the left or centre-left of the political spectrum, according to analysis by Fabian research director Tim Horton. Many fewer think of themselves (9%) or the party (5%) as centre-right or right.
The Fabian briefing paper identifies the LibDem MPs who would be most vulnerable to a Clegg-Cameron deal. Tim Horton offers a summary at Left Foot Forward, with more detail in the briefing paper on the Fabian website.
It shows that frontbenchers Sarah Teather and Jo Swinson, along with the five new LibDem MPs who gained seats from Labour last Thursday, could all lose their seats to Labour if just one in ten of current LibDem voters switched as a result of a LibDem deal to put David Cameron into office. Fifteen seats could be vulnerable if one in five LibDem voters switched to Labour - notably university seats where the party made significant gains in 2005.
In theory, some of these LibDems could try to appeal to Tory tactical voters to try and hold on after a Clegg-Cameron deal. But in doing so, they would risk reinforcing Labour's challenge and further alienating their own support. And the 2010 election was one in which a good deal of anti-Labour tactical voting will already have taken place.
Making a credible appeal for more Tory votes would be particularly difficult for MPs like Sarah Teather, who have sought to challenge Labour from its left. That strategy has won Teather 44% of the vote in Brent Central with Labour second on 41%. To seek to appeal to the 11% of Tory voters to help keep her in would mean Teather standing on her head, effectively seeking re-election as a centre-right anti-Labour candidate, perhaps risking a much greater swing back to Labour as a result.
If Nick Clegg does want to be Home Secretary, he may have to decide if costing poor Sarah Teather her seat would be a sacrifice worth making.
Little attention has been paid to the electoral implications of a Lib-Con deal for the Conservatives.
Horton's analysis shows that Labour would also be ahead in twenty Tory-held seats if just one in five LibDem voters switched to the only anti-Conservative party. (Even a LibDem-Lab switch of just one in twenty would be enough to win eight Tory seats).
Horton's analysis therefore also highlights some important nuances for the coming post-election political strategy debate about how Labour puts back together majorities in Labour-Tory marginals, especially in southern England.
Winning back voters who switched to the Tories will be important - with Labour especially losing support among C2 voters - but an effective strategy would also benefit from a stronger appeal to progressive voters who may be particularly up for grabs in the event of a Clegg-Cameron deal.