With the news last night that Don Foster, the MP for Bath, is going to stand down at the next General Election, that takes the total of Lib Dems voluntarily leaving Parliament to eight – almost 15 per cent of their Parliamentary Party.

This isn’t just a grim sign for Nick Clegg of his colleagues’ confidence in his electoral performance, it’s also a significant blow to the party’s main advantage at the ballot box: the personal vote.

The Lib Dems have long boasted of the ability of their MPs to build up majorities based on support for them as individuals. It’s one of the reasons cited by those who believe their number of seats will hold up better than their national vote in 2015.

In that sense, such appeal for an incumbent it’s a useful tool. But it’s also a weakness should those individuals decide to step down. If voters in Bath were encouraged to view themselves as Don Foster voters rather than instinctive Lib Dems, then the factor which gave him an 11,883 majority in 2010 may well leave those same voters open to persuasion by other parties once he’s gone.

That’s good news for Ben Howlett, the Conservative PPC in Bath, and yet more bad news for the Lib Dems.