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The boundary commissions in the United Kingdom are non-departmental public bodies responsible for determining the boundaries of constituencies for elections to the House of Commons, the Scottish Parliament and the National Assembly for Wales.[1] There are four separate boundary commissions:

  • Boundary Commission for England
  • Boundary Commission for Scotland
  • Boundary Commission for Wales (Welsh: Comisiwn Ffiniau i Gymru)
  • Boundary Commission for Northern Ireland

Each commission comprises four members, three of whom take part in meetings. The Speaker of the House of Commons is ex officio chairman of each of the boundary commissions. However, the Speaker does not play any part in proceedings, and a Justice is appointed to each boundary commission as Deputy Chairman Commissioner.


The commissions are currently established under the Parliamentary Constituencies Act 1986, most recently amended by the Parliamentary Voting System and Constituencies Act 2011. They were first established as permanent bodies under the House of Commons (Redistribution of Seats) Act 1944. The 1944 Act was amended in 1947 and then replaced by the House of Commons (Redistribution of Seats) Act 1949. The 1949 Act was amended in 1958 and 1979 and replaced by the 1986 Act; changes in legislation from 1944 to 1986 were generally incremental in nature. The 2011 Act under the Con-LibDem coalition government made substantial changes to the legislation governing constituency boundary reviews.

The Political Parties, Elections and Referendums Act 2000 under PM Tony Blair's government envisaged that the functions of the boundary commissioners would be transferred to the United Kingdom Electoral Commission, but this never transpired: the Local Democracy, Economic Development and Construction Act 2009 repealed the Act of Parliament (of 2000) effective from 1 April 2010.

United Kingdom Parliament constituencies

The Sixth Periodic Review of Westminster constituencies was launched on 4 March 2011 by the Boundary Commission for England,[2] the Boundary Commission for Scotland,[3] the Boundary Commission for Wales[4] and the Boundary Commission for Northern Ireland.[5] The Sixth Review would have resulted in 600 constituencies for the United Kingdom Parliament: a reduction from the 650 constituencies in existence at the General Election of 2010. The number of constituencies in each of the four home nations is calculated in proportion to the electorate using a formula set out by legislation. For the Sixth Review, the formula specified 502 constituencies in England, 16 constituencies in Northern Ireland, 52 constituencies in Scotland, and 30 constituencies in Wales.

In January 2013, parliamentary opposition to proposed legislative amendments recommended by this Sixth Review meant that the review was unable to be enacted because of a lack of coalition government consensus. Each Commission is required by law to conduct subsequent reviews of all constituencies in its respective part of the United Kingdom at least every five years.

Considerations and process

The boundary commissions are required to apply a set series of rules when devising constituencies.

Firstly, each proposed constituency has to comply with two numerical limits:

  • the electorate (number of registered voters) of each constituency must be within 5% of the United Kingdom electoral quota. The electoral quota is the average number of electors per constituency, defined as the total mainland electorate divided by the number of mainland constituencies, where "mainland" excludes four island constituencies: Orkney and Shetland, Na h-Eileanan an Iar (Western Isles), and two on the Isle of Wight.
  • the area of a constituency must be no more than 13,000 square kilometres (5,000 sq mi).

There are a small number of exceptions to the numerical limit on electorate which are specified in the legislation:

  • the four island constituencies are permitted to have a smaller electorate than the usual limit;
  • a constituency with an area of more than 12,000 square kilometres (4,600 sq mi) may have a smaller electorate than the usual limit; and
  • constituencies in Northern Ireland may be subject to slightly different limits under certain circumstances.

Having satisfied the electorate and area requirements, each commission can also take into account a number of other factors:

  • "special geographical considerations" including the size, shape and accessibility of a constituency;
  • local government boundaries;
  • boundaries of existing constituencies;
  • local ties which would be broken by changes to constituencies;
  • inconveniences resulting from changes to constituencies.

It is evident that the other factors can to an extent be mutually contradictory, and therefore each commission has discretion on how it applies them. In so doing, each commission aims for a consistent approach within a review.

When a commission publishes its proposals for public consultation, the consultation period is specified in that legislation:

  • for Initial Proposals, a twelve-week initial consultation period including a number of public hearings which offered an opportunity to give views orally;
  • after the Initial Proposals, a four-week secondary consultation allowing scrutiny of all comments submitted during the initial consultation; and
  • for Revised Proposals, an eight-week consultation period.

It has been normal practice for local government electoral wards to be used as building blocks for constituencies, although there is no legislative requirement to do so. In Scotland, the introduction of multi-member wards in 2007 has made it harder to do so, since these wards each have a large electorate, and therefore a collection of complete wards may not give an electorate that is close to the required average.

The law specifies that the electorate used during a review is the registered electorate at the time of the start of the review, and not the electorate at the end of a review, or the total population.

Boundary changes can have a significant effect on the results of elections,[6] but boundary commissions do not take any account of voting patterns in their deliberations, or consider what the effect of their recommendations on the outcome of an election may be.

Previous reviews of UK Parliament constituencies

Customarily, each commission conducted a complete review of all constituencies in its part of the United Kingdom every eight to twelve years. In between these general reviews, the commissions were able to conduct interim reviews of part of their area of responsibility. The interim reviews usually did not yield drastic changes in boundaries, while the general reviews generally did.

The most recent[7] general review in Wales was given effect by an order made in 2006,[8] in England by an Order from 2007[9] and in Northern Ireland by an Order from 2008,[10] with the new boundaries used for the May 2010 general election. The most recent general review in Scotland was given effect in 2005,[11] and the resulting constituencies were used in the May 2005 general election.

Under the previous rules, the number of constituencies in Great Britain (England, Wales, and Scotland) had to "not be substantially greater or less than 613", of which at least 35 had to be in Wales. The City of London was not to be partitioned and was to be included in a seat that referred to it by name. The Orkney and Shetland Islands were not to be combined with any other areas. Northern Ireland had to have between 16 and 18 constituencies.[12]

Under the earlier legislation, the terms of review were significantly different:

  • the total number of constituencies was not fixed (see above): each commission had limited discretion to specify the number in its part of the United Kingdom;
  • electorate was just one of several rules, rather than being a numerical limit which overrides other factors;
  • there was not previously a limit on the area of a constituency, but in practice no constituency has ever exceeded the 13,000 square kilometre limit introduced by the 2011 Act;
  • the consultation mechanism was significantly different: consultation periods only lasted four weeks, and could be followed by local inquiries;
  • reviews were only carried out every eight to twelve years instead of every five years.

At the 2010 general election there were 533 constituencies in England, 40 constituencies in Wales, 59 constituencies in Scotland and 18 constituencies in Northern Ireland providing a total of 650.

Devolved parliaments and assemblies

The boundary commissions are also responsible for reviews of boundaries for devolved parliaments and assemblies.

The procedure for reviews of constituencies and regions for the Scottish Parliament is set down by the Scotland Act 1998. That Act specifies that there are 73 constituencies for the Scottish Parliament: the Orkney Islands, the Shetland Islands and 71 others. The Act also specifies that the constituencies are grouped into eight regions to allow the return of list members elected by proportional representation to the parliament. The Boundary Commission for Scotland conducted a review of these boundaries between 2007 and 2010,[13] whose recommendations were implemented from 2011. Since the legislation requires different numbers of constituencies in Scotland for the United Kingdom Parliament and the Scottish Parliament, these two sets of areas do not fit together neatly. Responsibility for Scottish Parliament boundary reviews passed to the Local Government Boundary Commission for Scotland in May 2017.

The Government of Wales Act 2006 specified that the constituencies for the National Assembly for Wales were to be the same as those for the UK Parliament at Westminster. The Act required the Boundary Commission for Wales to group the constituencies into electoral regions, to allow the return of list members elected by proportional representation to the Assembly. The Boundary Commission for Wales's Fifth General Review resulted in revised Assembly constituencies and electoral regions. The Parliamentary Voting System and Constituencies Act 2011 removed the link between Westminster constituencies and National Assembly for Wales constituencies: replacement legislation is expected in time for the National Assembly elections in 2015.[14]

Section 33 of the Northern Ireland Act 1998 provides that the constituencies for the Northern Ireland Assembly are the same as the constituencies that are used for the United Kingdom Parliament, but there are six members rather than just one elected from each constituency.[15]

Implementation of recommendations

Once a commission has completed a review, it submits a report to the appropriate Secretary of State who puts forward legislation to the Parliament implementing the recommendations. Parliament may approve or reject these recommendations, but may not amend them. If Parliament approves the recommendations, then the Sovereign signs an order formalising the boundary changes which are to be used at the next general election. Any by-elections use the pre-existing boundaries.

Although for many years the legislation gave the Secretary of State the power to modify a commission's recommendations, this power was never exercised. This separates boundary making by a combination of structure and convention from those elected from the resulting electoral areas, thus significantly reducing any scope for gerrymandering.

Relationship with local government functions

The scope of the boundary commissions' work is limited to areas for election to parliaments and assemblies. Local authority areas and electoral areas are reviewed by the separate but similarly-named:

Changes to parliamentary boundaries do not themselves impact on which local councils are responsible for any area.

See also

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