6th boundary review (2015)

The sixth periodic boundary review was due to take place between 2010 and 2013, but was abandoned in early 2013. The sixth review would have been due to report by 2019, but was brought forward by the Parliamentary Voting System and Constituencies Act 2011 which changed the rules to require a boundary review every five years and amended the rules to equalise electorates between seats in England, Scotland, Wales and Northern Ireland, speed up the review process, fix the total number of seats at 600 and prioritise equality in electorate size over other concerns, including an absolute requirement for most seats to have an electorate within 5% of the quota.

The Boundary Commissions released provisional boundary recommendations in late 2011 and revised recommendations in 2012. Following the abandonment of the House of Lords reforms in the face of backbench Conservative and Labour opposition that left the government unable to pass a programme motion the Liberal Democrats announced they would no longer support the implementation of the boundary review when the Commissions reported. In January 2013 Labour and the Liberal Democrats forced through an amendment to the Electoral Registration and Administration Bill that cancelled the review, setting the next review of boundaries at 2018.


As with most boundary reviews, the overall effect of the review would have been to favour the Conservative party. The sixth review would have fixed the number of seats at 600, removing the current ratchet effect of the boundary review rules and meaning that a party would require 301 MPs for an overall majority.

The boundary recommendations produced some drastic changes in boundaries due to the reduction of seats from 650 to 600, requiring major changes in many areas. The Boundary Commission in England also chose not to divide council wards in its initial recommendations, which in many areas required them to cross local authority boundaries or divide communities in order to meet the 5% quota without dividing council wards.

The overall net effect would have been to reduce the number of Conservative seats by 4, reduce the number of Labour seats by 36, reduce the number of Liberal Democrat seats by 6 and the number of seats by other parties by 4. This means that had the 2010 election been fought on the revised boundaries produced by the 6th review the Conservatives would have won a small overall majority of 4 seats, rather than there being a hung Parliament.

On the exiting current boundaries the Conservatives need a lead of 11.1% to win an overall majority on a uniform swing. They need a lead of 4.1% to be the largest party. Labour need a lead of 2.9% to get an overall majority. If the two main parties had equal shares of the vote Labour would have 53 seats more than the Conservatives. On the revised boundaries the Conservatives would have needed a lead of 7% to win an overall majority, they would have needed a lead of 1.4% to be the biggest party. Labour would needed a lead of 4.7% to win an overall majority. If the two main parties had equal shares of the vote Labour would have had 16 seats more than the Conservatives (Note these are requirements for a uniform swing between Conservative and Labour, if the Liberal Democrat vote in 2015 falls then both parties need smaller leads to secure a majority - see the FAQ here.

Full notional results for the 2010 election on the revised boundaries at the time the review was abandoned are available as a Google Spreadsheet here.

The revised recommendations published by the Commissions before the review was halted can be found here (Scot, Wal, NI, Eng).

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