The perils of projecting the impact of boundary changes from previous election results

There’s been an understandable flurry of interest in The Guardian’s reported projections of what boundary changes might mean for the parties, but there are two major caveats about the nature of such projections.

From what I’ve seen, Lewis Baston (as I would expect) has done the numbers well, but not only do we not yet have the actual boundaries on which to make projections but also projections based on looking at previous election results have a decidedly ropey record when it comes to Liberal Democrats MPs.

That is because the party’s voting support is far less polarised demographically than that of Labour or the Tories, so knowing the sort of area being added to or removed from a constituency acts as a far less helpful guide to what that might mean for Liberal Democrat support at the next election than it does for either of them. It’s also because of the related ability of MPs in particular (and other candidates to a lesser degree) to therefore build up support in areas that previously looked very weak for the party.

There is nothing new in this phenomena, but the 2010 general election provided one very striking example in Brent Central. Many outsiders were in advance confidentially predicting that Sarah would be defeated because of the apparent large Labour majority in that new seat, based on calculations using previous local and general election results.

However, one of the main reasons for Sarah choosing to fight that seat was the polling the party did (and which I did the analysis for) during the last Parliament. At the time when to the outside world those calculations were showing a large Labour majority, the actual polling was showing something very different – a seat where the Liberal Democrats were the narrow favourites to win. Alas, the other part of my polling analysis also turned out right – that the odds of winning Hampstead & Kilburn were slightly less good.

This sort of experience has been repeated many times in the past, with Liberal Democrat MPs seeing off apparently massive odds because the nominal calculations didn’t actual reflect the realities on the ground. (Long-standing Scottish members may well remember the case of Malcolm Bruce’s boundaries in the 1990s in particular…)

Fewer seats means bigger seats, which means most Liberal Democrat MPs will have to fight new territory. That, however, is nothing new and in previous boundary changes it has not caused significant problems for the party. It’s not the boundaries that will decide the fate of the bulk of the Parliamentary Party; it’s the party’s performance in government.