Constituency boundary reviews and the number of MPs
This briefing summarises the rules and procedures for boundary changes for parliamentary constituencies. It also examines how the number of constituencies and MPs have changed over time.
The House of Commons is now fixed at 650 seats.
There had been steady increase in the number of Parliamentary constituencies from 625 in 1950, to 659 from 1997. It remained at 659 until 2005. In 2005 the number dropped to 646. This followed the re-establishment of the Scottish Parliament and the associated reduction in the number of Scottish seats in Westminster. In 2010 the number of seats increased to 650, the current number.
Boundary reviewsParliamentary constituency boundaries are reviewed periodically. This is principally so that constituencies are altered occasionally to take account of changes in population. Changes are also made to reflect local government boundary changes, so that administrative boundaries coincide as much as possible.
Boundary CommissionsThe reviews are undertaken by independent Boundary Commissions. There are four Commissions, one for each part of the United Kingdom. The Commissions are independent of Government but must follow the Rules of Redistribution set out in legislation and decided by Parliament.
An important part of reviews is the public feedback on proposals. When a Commission publishes a set of proposals it triggers a round of public consultation. There are up to three rounds of consultation.
Background to reviewsThe Commissions and the Rules they must follow were first established in 1944. The Rules guaranteed a minimum number of seats for Scotland, Wales and Northern Ireland and instructed the Boundary Commission for England to maintain the number of seats broadly at the existing level.
The Rules of Redistribution were amended several times over the years by Parliament, but the process remained broadly the same. The Commissions had to create seats close to the electoral quota but had discretion to deviate based on other considerations, such as local ties and geographical features.
There had been concern since the 1970s that the Rules of Redistribution needed amending. There had been an ever-increasing number of seats and the difference between the electorates of the smallest and largest seats had grown.
New Rules introduced in 2011 were meant to reduce the size the House of Commons and fix it at 600 seats and ensure the electorates of each seat would be similar. Two reviews were held on the 2011 Rules. Neither was implemented. The Rules were altered again in 2020.
The current RulesThe number of constituencies in the House of Commons is now fixed at 650. The number of seats allcoated to each part of the UK is allocated proportionally based on the registered Parliamentary electorate. There is no longer a guaranteed minimum for any country.
Constituencies must have an electorate within 5% of the ‘electoral quota’. The quota is the average number of Parliamentary electorate per constituency. There are five island seats that are exempt from the 5% rule: Orkney and Shetland, Na h-Eileanan an Iar, Ynys Môn, and the two seats allocated to the isle of Wight.
Commissions must give primacy to the 5% rule but may also consider other factors. These are existing Parliamentary constituency boundaries, local ties, local government boundaries and special geographical considerations, such as size, shape and accessibility of a constituency.
The 2023 ReviewThe allocation of seats for the 2023 Review was:
- England 543 (+10)
- Scotland 57 (-2)
- Wales 32 (-8)
- Northern Ireland 18 (no change)
The 2023 Review was completed in June 2023.
The latest review of boundaries, the 2023 Review was completed in June 2023. Their final recommendations will be implemented automatically. This is done by the Government submitting a single draft Order in Council to the Privy Council for approval by the King. Neither Parliament nor the Government can alter the Commissions’ recommendations and there are no votes in Parliament. The Parliamentary Constituencies Order 2023 was approved in November 2023.
The new boundaries will be used at the next general election after the Order in Council has been approved. By-elections before the general election use the existing boundaries.
Details of the review can be found on the Commissions’ websites: