By Tim Smith
As this author warned here, some of the assumptions that incumbency advantage would prevent a poor result for the Liberal Democrats at the election were flawed. As the post suggested, the party did indeed do far worse than the projection that they would hold onto at least 25 seats. As David Steel said, decades of progress were reversed with the party finishing up with just eight seats, the lowest since 1970, and it was arguably its worst result since 1959 in terms of share of the vote. The party lost all of its seats in its strongest English region, the South West, and all but one of its eleven seats in Scotland, another traditional stronghold for the party. Despite this, analysis in this post of the results of the election show that the large incumbency advantage the party has traditionally relied on has not gone away, but that it was not enough on its own to prevent a disaster.
At the election, the Liberal Democrat share of the vote fell in all 57 seats the party won in 2010. The smallest decline was in East Dunbartsonshire (2.4%); the largest was in Brent Central (35.8%), with a mean decline of 15.7%, slightly worse than the average in Great Britain. The table below shows the change in the Lib Dem vote from 2010 to 2015 in various categories of constituencies.