Constituencies of the Parliament of the United Kingdom

The number of seats rose from 646 to 650 at the 2010 general election after proposals made by the boundary commissions for England, Wales, and Northern Ireland (the Fifth Periodic Review of Westminster constituencies) were adopted through statutory instruments. Constituencies in Scotland remained unchanged at the 2010 election, as the Boundary Commission for Scotland had completed a review just before the 2005 general election, which had resulted in a reduction of 13 seats.

The most recent boundary review was conducted in 2023, with changes to the boundaries of constituencies across the UK. As part of the review to reflect population changes, England gained ten seats, while Wales lost eight seats, and Scotland lost two seats, while Northern Ireland's number of seats remained the same.

Primary legislation provides for the independence of the boundary commissions for each of the four parts of the UK, the number of seats for each of the countries, permissible factors to use in departing from any old boundaries, and a strong duty to consult. The Fifth Review was governed by the Parliamentary Constituencies Act of 1986. Under the Parliamentary Voting System and Constituencies Act 2011, as amended by the Parliamentary Constituencies Act 2020, the number of MPs is now fixed at 650. The Sainte-Laguë formula method is used to form groups of seats split between the four parts of the United Kingdom and the English regions (as defined by the NUTS 1 statistical regions of England).

Overview

The table below gives the number of eligible voters broken down by constituent country, including the average constituency size in each country.

As of 2023, every recommended constituency must have an electorate as at 2 March 2020 that is no smaller than 69,724 and no larger than 77,062. The exceptions to this rule are five 'protected' constituencies for island areas: Orkney and Shetland, Na h-Eileanan an Iar, Ynys Mon, and two constituencies on the Isle of Wight. These consequently have smaller electorates than the lower limit for other constituencies.

Geographical size of constituencies