By-elections take place when an MP steps down or dies. Here are seven that have shifted British politics.
Four senior Liberal Democrat politicians defeated in the general election, including former business secretary Vince Cable, have turned down offers of a peerage from Nick Clegg in the dissolution honours list.
It was a night of shocks and – for a number of well-known political faces – particularly painful defeats, as Labour was crushed in Scotland and the Liberal Democrats, too, lost a number of their star players across the UK, alongside other high profile surprises.
Nick Clegg has defeated an attempt by senior Liberal Democrats to match the Tories by guaranteeing to hold a "seductive" referendum on Britain's EU membership in the next parliament.