The UK Liberal Democrat party is one of the oldest political parties in the world, tracing its roots back to the Whigs of the era of William of Orange.
The modern incarnation stems from the merger of the Liberals with the SDP in the 1980s - in each election since then they have steadily increased their presence in the House of Commons, gaining 62 seats in the 2005 general election.
Their policies can be broadly described as social-democratic, with a libertarian bent - they have mooted the idea of decriminalising recreational drugs, whilst arguing for a rationalisation of the currently confused status of the various components of the United Kingdom.