Boundary review 2023: Which seats will change in the UK? 

What are boundary reviews?

Constituency boundaries are reviewed periodically to make sure that constituencies are all roughly a similar size and respect local ties between areas. The reviews alter constituencies to reflect rising and falling populations and changes in the boundaries of the electoral wards that comprise them.

The current constituency boundaries were designed based on electorates in 2000 and have been in use since 2010. For more information on the process, see Commons Library research briefings on boundary reviews and public consultations.

The 2023 boundary review is stricter than previous ones when looking at how much electorates can vary in each constituency. Constituencies must now have populations within 5% of the ‘electoral quota’ of 73,393, except for five protected island seats such as Ynys Môn. Previously, closeness to the quota had been one of several factors and had not been limited to a set range.

How will seats change after the 2023 review?

Most constituencies will have new boundaries. We have measured the size of the changes by looking at the proportion of the population and residential premises in existing constituencies that move into new constituencies under these recommendations.

Overall, just over half of the existing constituencies (332) will be very similar to their closest successor (with over 90% of premises in the same constituency before and after the change).

No change

65 seats (one in 10) will have no change to their boundaries, although four of these will have a new name. The remaining 585 seats will have at least some change.

Small change

40 seats will have only a small change to their boundaries (in some cases affecting only a few premises).

Enlarged constituencies

76 seats will be enlarged compared with their current boundaries. This means that the new constituency covers all (or almost all) of the current constituency’s area, but also extends to areas that used to be part of different constituencies. These seats would mostly have been too small to meet the minimum electorate threshold in their current form. An example, Clacton, is shown in the map below.

Reduced constituencies

73 seats will be reduced in size compared with their current boundaries. This means that they give up areas to other new constituencies but gain no (or almost no) new areas. These seats would mostly have had electorates higher than the maximum threshold in their current form. An example, Sheffield Central, is shown in the map below.

Information on each constituency can be viewed in the dashboard above or in the data tables.

Which constituencies will be abolished?

A constituency is sometimes said to be “abolished” if its area is split between many surrounding constituencies and/or there is no obvious successor.

There is no definitive list of abolished constituencies, but we can look at constituencies that will be split the most. The table below shows the 15 current seats with the lowest similarity to their ‘closest successor’ – the new constituency that resembles them most closely.

Newcastle-upon-Tyne North will be heavily changed despite retaining the same name. This illustrates that whether or not a constituency will keep the same name in the future is not a good indicator of whether the boundaries will change.

The map image below shows Ogmore in South Wales, which will be split between five constituencies with no close successor. The portion moving to Cardiff West is small (1% of premises).

What happens next?

There is no formal parliamentary stage or vote on the final recommendations and Parliament is unable to amend them.

The Government must now draw up a single draft Order in Council to implement the recommendations. Orders in Council are Orders that have been approved at a meeting of the Privy Council personally by the King.

The Government must submit the draft Order to the Privy Council for approval “as soon as reasonably practicable”. The legislation states this must be no later than four months after the final reports have been laid in Parliament unless there are exceptional circumstances.

The draft Order must contain the final recommendations of the Boundary Commissions. The Government cannot make changes.

Download the data

Download data in Excel (684KB)

The data file shows details of changes for each constituency in the UK. It provides:

• A summary of changes for each current constituency, including the closest successor
• Details of all overlaps between current constituencies and new constituencies
• A list of wards in each new constituency based on 2023 ward boundaries (including proportions for split wards)

Notes on calculations

We have calculated differences between current and proposed constituency boundaries by looking mainly at address locations and populations.

Residential premises

The address analysis is based on the locations of residential premises. There are some differences between old and new constituencies that do not contain residential premises.

For example, Lincoln’s constituency boundary has a small change, but the area gained by the new Lincoln constituency contains no residential premises. There are 22 such cases in different parts of the UK. These are highlighted in the data file above.

Population

The estimated population of overlaps between old and new constituencies is based on 2021 Output Area Centroids (for England and Wales), 2011 Datazone Centroids (for Scotland), and the address-weighted centroids of 2021 Datazones (for Northern Ireland).

This measure is less fine-grained than residential premises, and for 69 small overlaps it is not possible to calculate a population using this method. Because of this, the map and dashboard above use the percentage of residential premises as their primary measure.

Geographical area

The data file also provides a measure of the geographical size of overlap between old and new constituencies. This is not always a useful measure of changes, because large areas can be sparsely populated, and small areas can be densely populated.

For example, Darlington constituency will be four times larger after the boundary review, but as the gained area is sparsely populated, the population will grow by only 5.6%.

Electorate

No figures are presented for changes in electorate, because it’s not possible to calculate electorates for many of the small overlaps between old and new constituencies.

Data sources and attributions

New constituency boundaries are available from the four Boundary Commissions:

• Boundary Commission for England
• Boundary Commission for Scotland
• Boundary Commission for Wales
• Boundary Commission for Northern Ireland

The analysis contains Ordnance Survey data © Crown copyright and database rights [2023] OS [AC0000813358]

About the author: Carl Baker is a statistician specialising in health and geography at the House of Commons Library. Neil Johnston is researcher specialising in elections at the House of Commons Library.