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The number of seats

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 reviews

Parliamentary 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.

Progress of the 2023 Review can be found in the Library briefing, Parliamentary boundary reviews: public consultations.

Boundary Commissions

The reviews are undertaken by independent Boundary Commissions. There are four Commissions, one each for the four nations 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 reviews

The 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 of Redistribution introduced in 2011 were meant to reduce the size the House of Commons and fix it at 600 seats. They would also ensure the electorates of each seat would be similar.

Two reviews were held that were meant to reduce the size of the House of Commons to 600 seats. Neither was implemented. The Rules of Redistribution were altered in 2020 to fix the House of Commons at 650 seats but the primacy of the rule that constituencies should be of a similar size was retained.

The current Rules

The number of constituencies in the House of Commons is now fixed at 650. The number of seats between the four nations of the UK are allocated proportionally. This is based on the registered Parliamentary electorate in each part of the UK. 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 latest review, the 2023 Review, was started in January 2021. It must be completed by 1 July 2023. Once completed the final recommendations of the four Commissions must be implemented automatically.

The allocation of seats between each of the nations of the UK is calculated based on the proportion of the UK registered electorate in each country:

  • England                 543      (+10)
  • Scotland                57        (-2)
  • Wales                    32        (-8)
  • Northern Ireland    18        (no change)

Details of the review can be found on the Commissions’ websites:

Documents to download

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