There are 650 constituencies in the United Kingdom, each electing a single Member of Parliament to the House of Commons at least every five years.Voting last took place in all 650 of those constituencies at the United Kingdom general election on 7 May 2015. 328 are held by the Conservative Party, 229 are held by the Labour Party, 54 are held by the Scottish National Party, 9 are held by the Liberal Democrats, 3 are held by Plaid Cymru, 1 is held by UKIP, 1 is held by the Green Party of England and Wales, 5 are independents and there are 18 Northern Ireland seats held by different parties, and 1 is vacant. In addition there is the constituency of the Speaker.
The number of seats rose from 646 at the 2005 general election after proposals made by the boundary commissions for England, Wales and Northern Ireland were adopted through statutory instruments. Constituencies in Scotland remained unchanged, with the Boundary Commission for Scotland having completed a review shortly prior to the 2005 general election.