Parliamentary constituency boundaries are periodically reviewed so that representation reflects changes in the distribution of the electorate. The process is carried out by independent Boundary Commissions for the four parts of the UK.
Why boundaries change
Populations and electorates do not remain static. Some areas grow while others shrink. Boundary reviews redraw constituencies under rules set by Parliament, including requirements concerning electorate size.
There are still 650 seats
The rules used for the 2023 Review retained 650 House of Commons constituencies. The resulting distribution was 543 in England, 57 in Scotland, 32 in Wales and 18 in Northern Ireland.
Public consultation
The commissions publish proposals and invite representations. In England, for example, the review included written consultation and public hearings before final recommendations were produced.
Why boundaries complicate election comparisons
When constituency boundaries change, a seat with the same or a similar name may contain a different electorate. Comparing its result directly with the previous election can therefore be misleading.
Analysts sometimes calculate notional results: estimates of how the previous election might have looked on the new boundaries. These are analytical reconstructions, not actual election results.