Here’s an unlikely parallel – between the Liberal Democrats and the French Communist Party. In the run-up to the 1981 Presidential election campaign, polls gave the PCF cause for encouragement. But as with the Lib Dems in 2010, it proved to be a false dawn.

Also as with the Lib Dems, the PCF took a junior role in the government – filling a number of cabinet posts.

French conservatives were aghast, condemning Francois Mitterrand for doing a deal with the devil. They needn’t have worried – the experience of government was not a happy one for the PCF. Within a few years they were out of power and well on the way to irrelevance.

Coalition is rarely a comfortable experience for minor parties, but what is less appreciated is that it can be a downright fatal one. The Communists in France, the Free Democrats in Germany and the Progressive Democrats in Ireland are all examples of the worst that can happen.

Tonight, the Lib Dems are facing a similar fate.