You are here:

House of Commons Library

Constituency boundary reviews and the number of MPs

Published Thursday, February 25, 2016

This House of Commons Library briefing explains how Parliamentary constituency boundaries are reviewed. The next review will reduce the size of the House of Commons to 600.

Jump to full report >>

Constituency boundaries are kept under regular review to ensure Members of Parliament represent roughly the same number of constituents at Westminster.

The current boundary review

The Boundary Commissions for England, Northern Ireland, Scotland and Wales launched their reviews on 24 February 2016. They must report in September 2018.

Who reviews constituency boundaries?

The reviews are carried out by the Boundary Commissions, one for each part of the UK. These are independent and impartial bodies that propose constituencies that must meet the Rules for Redistribution set out in statute.

How are constituency boundaries reviewed?

The Boundary Commissions propose changes to existing constituency boundaries based on the Rules for Redistribution. They consult the public on their proposals, and may revise their initial recommendations. After they submit their final reports, the Secretary of State must lay these before Parliament. The Secretary of State must then lay before Parliament a draft Order in Council to give effect to the proposed boundary changes. This Order requires the approval of both Houses of Parliament.

What are the Rules for Redistribution?

The Rules are contained in the Parliamentary Constituencies Act 1986. They were amended by the Parliamentary Voting System and Constituencies Act 2011 to include the requirements that:

  • the House of Commons must have 600 seats; and
  • all constituencies (with the exception of four island seats) must have electorates within 5% of the electoral quota. This is the total number of voters in the UK divided by the total number of constituencies (with the exception of the four island seats and their electorates). For the 2018 Review, this means constituencies must have electorates between 71,031 and 78,507.

The Rules also state that each constituency must be wholly within one of the four parts of the UK, and cannot be larger than 13,000 square kilometres; and that the Boundary Commissions may take into account certain considerations such as local government boundaries and existing constituency boundaries when proposing constituencies.

How many MPs were there before?

Historically, the number of MPs has varied, but it has been over 600 since the 19th century. There are currently 650 MPs.

What happened in 2013?

The 2013 Review was the first to use the new Rules for Redistribution and would have reduced the size of the House of Commons to 600. The review was halted after then Deputy Prime Minister Nick Clegg announced he would instruct his party to vote against the implementation of the Boundary Commissions’ proposals. A vote was avoided; the date the Commissions were required to report was changed to 2018.

What is the history of boundary reviews?

Regular reviews of constituency boundaries have been carried out since 1944, although there have been some changes to the timing, the implementation and the Rules for the reviews. Scotland and Wales were historically over-represented at Westminster. Scotland lost this position in 2001, and Wales will too after the next review is implemented.

Does everyone support the Rules for Redistribution?

The new Rules for Redistribution have raised some concerns. The 2013 Review proved disruptive to existing constituency boundaries. To avoid this disruption, some argue that the Boundary Commissions should be allowed to propose more unequal constituencies; and should split wards when proposing constituencies. There have also been calls for using population data instead of the electoral register, which is incomplete and may prove more incomplete after Individual Electoral Registration took effect in December 2015 (for more information, see Library Briefing Paper 6764 Individual Electoral Registration). The idea that the Boundary Commissions should create more marginal seats has also been discussed.

Reforming the Rules for Redistribution would require primary legislation.


Commons Briefing papers SN05929

Authors: Elise Uberoi; Isobel White

Topic: Elections

Share this page

Stay up to date

  • Subscribe to RSS feed Subscribe to Email alerts Commons Briefing papers

House of Commons Library

The House of Commons Library provides research, analysis and information services for MPs and their staff.