The floor of the House is the broad gangway which separates the two sets of benches in the House of Commons chamber.
Crossing the floor is the term used to describe a Member of Parliament's decision to leave one political party to join another.
In 1904, Sir Winston Churchill crossed the floor, leaving the Conservative Party to join the Liberal Party. He then returned to the Conservatives in the 1920s.
In 2007, Quentin Davies left the Conservatives to join Labour, arguing that his former party appeared "to have ceased collectively to believe in anything, or to stand for anything".