LONDON — Their poll ratings are terrible and their leader is widely mocked, but the Liberal Democrats, the traditional minnows of British politics, have chalked up one striking success: they have stayed part of a durable coalition government.

Before 2010, when an inconclusive election prompted an unlikely alliance between the centrist Liberal Democrats and the dominant Conservatives, Britons associated coalition governments with the unstable, revolving-door politics sometimes seen in Continental Europe.

Yet Britain’s first formal coalition since World War II has functioned surprisingly well, navigating policy differences, putting in place austerity measures and now presiding over modest economic growth.

“All the dire warnings given before the general election, particularly by the Conservatives and by the press, about a coalition being chaotic and messy and making Britain ungovernable do not seem to have come true,” said Tim Bale, a professor of politics at Queen Mary University of London.