5th boundary review (2010)

The fifth periodic boundary review took place between 2001 and 2007 in England, Wales and Northern Ireland and was implemented at the 2010 election (the boundaries for Scotland had already been reviewed for the 2005 election, in order to reduce the number of seats under the Scotland Act).

Summary

As with most boundary reviews, the overall effect was to favour the Conservative party. The fifth review increased the number of members of the Commons from 646 to 650, meaning that a party would require 326 MPs for an overall majority (although since Sinn Fein MPs do not take their seats, in practical terms an overall majority is slightly lower).

The boundary changes resulted in the creation of thirteen new seats (10 Conservative seats and 3 Liberal Democrat seat) and the abolition of nine seats (6 Labour, 2 Conservative and 1 Liberal Democrat). Twenty seats would notionally have been won by different parties under the new boundaries. These mainly favour the Conservative party, who would have won an extra 13 seats that are currently held by Labour or the Liberal Democrats while only losing 5 seats they actually won. Labour would have won 6 seats that are currently held by the Conservatives or Plaid Cymru, but would have lost 12 seats to Labour or the Liberal Democrats. The Lib Dems would have won Oxford East on the new boundaries, but would have lost 2 seats they currently hold to the Conservatives.

The net effect of the changes was to increase the number of Conservative seats by 16, increase the number of Liberal Democrat seats by 1, decrease the number of Labour seats by 12 and decrease the number of Plaid Cymru seats by 1.

Summary of effects
New seats

Broadland - Conservative majority 5121 (10.6%)
Chelsea and Fulham - Conservative majority 10724 (30.2%)
Chippenham - Lib Dem majority 1260 (2.7%)
Derbyshire Mid - Conservative majority 2971 (6.8%)
Devon Central - Conservative majority 1744 (3.7%)
Filton and Bradley Stoke - Conservative majority 1201 (2.9%)
Kenilworth and Southam - Conservative majority 8992 (19.5%)
Meon Valley - Conservative majority 1990 (4.1%)
Northamptonshire South - Conservative majority 10617 (24.3%)
St Austell and Newquay - Lib Dem majority 630 (1.6%)
Witham - Conservative majority 7045 (16%)
Wyre and Preston North - Conservative majority 14567 (28.7%)
York Outer - Lib Dem majority 1821 (4.5%)

Abolished seats

Birmingham Sparkbrook and Small Heath - Roger Godsiff (Labour)
Brent East - Sarah Teather (Liberal Democrat)
Eccles - Ian Stewart (Labour)
Hornchurch - James Brokenshire (Conservative)
Knowsley North & Sefton East - George Howarth (Labour)
Normanton - Ed Balls (Labour)
Sheffield Hillsborough - Angela Smith (Labour)
Tyne Bridge - David Clelland (Labour)
Vale of York - Anne McIntosh (Conservative)

Seats changing hands

5 Conservative seats notionally gained by Labour:
Lancaster and Fleetwood (was Lancaster & Wyre)
Croydon Central
Milton Keynes North (was Milton Keynes North East)
Hammersmith (was Hammersmith & Fulham)
Northampton South

11 Labour seats notionally gained by the Conservatives:
Somerset North East (was Wansdyke)
Staffordshire Moorlands
Selby and Ainsty (was Selby)
Gillingham and Rainham (was Gillingham)
Portsmouth North
Thanet South
Sittingbourne and Sheppey
Rochester and Strood (was Medway)
Wirral West
Ealing Central and Acton (was Ealing, Acton & Shepherd's Bush)
Enfield North

1 Labour seat notionally gained by the Liberal Democrats:
Oxford East

2 Liberal Democrat seats notionally gained by the Conservatives:
Solihull
Somerton and Frome

1 Plaid Cymru seat notionally gained by Labour:
Arfon (was Caernarfon)

While the new boundaries favoured the Conservative party, the effect was marginal. Under the previous boundaries the Conservatives would have required a swing of 2.2% to rob Labour of a majority, 4.8% to become the largest party and 7.4% to gain an overall majority. On the new boundaries they required a swing of 1.5% to deprive Labour of a majority, 4.5% to become the largest party, and 6.9% to gain a majority.

Of the nine MPs whose seats were abolished in the fifth review, six were selected and returned in a neighbouring constituency. One (James Brokenshire) was selected for a seat elsewhere in the country, one (David Clelland) was selected for a neighbouring seat but instead chose to retire. Only one (Ian Stewart) was left without a seat to contest. He subsequently became the first elected mayor of Salford.

Full notional results for the 2005 election can be downloaded here.
The Boundary Commission for England's full report for the fifth review can be downloaded here