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Boundary Reviews

Parliamentary constituency boundaries are reviewed periodically. This is principally so that constituencies are altered occasionally to take account of changes in population over time. Changes are also made to reflect local government boundary changes, so that administrative boundaries coincide as much as possible.

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.

The latest review, known as the 2023 Review, was launched by the four Commissions on the 5 January 2021. Details of the review can be found on the Commissions’ websites:

The final recommendations of the 2023 Review must be handed to the Speaker of the House of Commons by 1 July 2023.

The number of seats is fixed at 650. 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)

Each seat must be within 5% of the electoral quota. The quota is the mean average electorate per seat. Five constituencies are exempt from this rule: Orkney and Shetland, Na h-Eileanan an Iar, Ynys Môn and the two seats on the Isle of Wight. This means all constituencies (except the five protected islands seats) will have to have electorates of 69,724 to 77,062 Parliamentary electors, based on the March 2020 electoral registers used for the review. 

The Commissions formulate proposals, using the Rules of Redistribution, which are then published for public consultation. There are currently two rounds of consultation on a Commission’s initial proposals, which include public hearings.

The Commissions may then alter their recommendations. If they decide to make alterations and publish revised recommendations, then another stage of consultation takes place. A report with the final recommendations must be handed the Government at the end of the review.   

Once the Commissions hand over their reports their role in the process ends. At the same time as handing the reports to the Speaker the Commissions must send copies to the UK Government. The Government must then draw up the draft Order in Council to implement the recommendations.

The Government cannot alter the final recommendations. There is no vote in Parliament on the draft Order, meaning that the implementation of the Commissions’ final recommendations is automatic.

Background to periodical reviews

The House of Commons (Redistribution of Seats) Act 1944 established permanent Commissions, the Rules of Redistribution, and the requirement to undertake regular reviews. The legislation resulted from the recommendations of the Speakers Conference of 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.

The number of seats

There was a 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 because of the reduction in the number of Scottish seats at Westminster, following devolution and the re-creation of the Scottish Parliament. The number rose again in 2010 following the implementation of the Fifth Periodical Boundary Review of Parliamentary constituencies. Since the 2010 General Election there have been 650 seats.

There had been concern since the 1970s that the Rules of Redistribution needed amending to prevent the ever-increasing number of seats and the differential electorates between seats. New Rules of Redistribution introduced in 2011 were meant to reduce the size the House of Commons and fix it at 600 seats. This change was never implemented and new Rules introduced in 2020 fix the House of Commons at 650 seats (see below).

Changes to the Rules in 2011

Following the 2010 General Election, the Coalition Government announced that it would bring forward a Bill on electoral reform which would make provision for the creation of a fixed number of seats, 600.

It also changed the Rules to make the primary consideration that seats had equal sized constituencies. Constituencies had to be within 5% of the electoral quota with a single quota for the whole of the UK. The requirement to be within 5% of the quota over-rode other considerations.

Four island constituencies were exempt from the constituency size requirements (Orkney and Shetland, Na h-Eileanan an Iar and two seats on the Isle of Wight). It also made changes to other aspects of the process, such as public consultations.

The first review under the new rules was meant to be completed in 2013. The review was abandoned in January 2013 before final recommendations were produced, and a new deadline for final recommendations was set for 1 October 2018. The reports of the Boundary Commissions were handed to the Government in September 2018.

2020 changes

In March 2020 the Government announced that it would not implement the net reduction in the number of seats in the House of Commons to 600 and instead it would introduce a Bill to amend the Rules of Redistribution.

The Parliamentary Constituencies Bill 2019-21 was introduced on 19 May 2020. The Bill passed its final Parliamentary stages on 26 November 2020 and received Royal Assent on 14 December 2020.

The key changes of the Parliamentary Constituencies Act were:

  • It abandoned the 2018 Review and therefore cancelled the reduction of the size of the House of Commons to 600 seats;
  • The House of Commons is fixed at 650 seats (but the calculation of the allocation of seats between the countries of the UK remains based on the proportion of the UK registered electorate in each country);
  • The next review, due to start in 2021, will have to be completed by the Boundary Commissions by 1 July 2023. It will be based on the number of registered electorates as of 2 March 2020;
  • The next review after the 2023 Review will have to be completed by 1 October 2031; with subsequent reviews required to report by the 1 October every eight years thereafter;
  • Recommendations of the Boundary Commissions will be no longer require Parliamentary approval and government ministers will have no power to alter recommendations. The final recommendations must be implemented as set out in the Commissions’ final reports. This provision became known as ‘automaticity’;
  • The public consultation phase was amended to allow for public hearings later in the consultation process.
  • The Boundary Commissions have more flexibility to use local government and ward boundaries that have yet to come into force.
  • Ynys Môn was added as an exempt seat.

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