2018 periodic review of Westminster constituencies

The 2018 periodic review of Westminster constituencies was an ultimately unfruitful cycle of the process by which constituencies of the House of Commons of the United Kingdom are reviewed and redistributed. The four UK boundary commissions carried out their reviews between 2016 and 2018, but their recommendations were not taken up by the government and were formally laid aside in 2020.

The boundary commissions were to take into account revised rules for the number and size (electoral quota) of constituencies. The proposed changes included having a total of 600 seats rather than 650, as agreed by Parliament in 2011 to meet a reformist aim of the 2010–2015 coalition agreement.

The 2013 periodic review of Westminster constituencies began in 2011 and was intended to be completed by 2013, but a January 2013 vote in the House of Commons stopped the process. The commissions re-commenced their drawing of new boundaries from scratch in 2016, and completed their work in September 2018. Although the proposals were immediately laid before Parliament they were not brought forward by the government for approval. Accordingly, they did not come into effect for the 2019 election, which was contested on 12 December 2019 using the constituency boundaries in place since 2010, as constituted by the fifth periodic review.

The 2018 Review was formally abandoned with the passing of the Parliamentary Constituencies Act 2020, which received Royal Assent on 14 December 2020. The following reviews began in 2021 and concluded in 2023.