account of the extraordinary wartime circumstances came ten years after the preceding election). This has been attributed to the 2009 expenses scandal and the fact there was talk that redundancy-style payments for departing MPs might be scrapped after the election. In all, 149 MPs (100 Labour, 35 Conservatives, 7 Liberal Democrats, 2 Independents, 1 Independent Conservative and 1 member each from the SNP, Plaid Cymru, the DUP, and the SDLP) decided not to contest the election. Additionally, three seats were vacant at the time of the dissolution of Parliament; two due to the deaths of Labour MPs and one due to the resignation in January 2010 of a DUP member. Boundary changes Each of the four national boundary commissions is required by the Parliamentary Constituencies Act 1986 (as amended by the Boundary Commissions Act 1992) to conduct a general review of all the constituencies in its part of the United Kingdom every eight to twelve years to ensure the size and composition of constituencies are as fair as possible. Based on the Rallings and Thrasher studies using ward by ward data from local elections and the 2005 general election, the new boundaries used in 2010 would have returned nine fewer Labour MPs had they been in place at the previous election; given that there are to be four more seats in the next parliament this nationally reduces Labour's majority from 66 to 48. Pursuant to Boundary Commission for England recommendations, the number of seats in England increased by four, and numerous changes were made to the existing constituency boundaries. Northern Ireland continued to elect 18 MPs, but minor changes were made to the eastern constituencies in accordance with the Northern Ireland Boundary Commission's recommendations. For the first time, these changes include the splitting of an electoral ward between two constituencies. Following the recommendations of the Boundary Commission for Wales, the total number of seats remained at 40, although new seats caused by radical redrawing of boundaries in Clwyd and Gwynedd were fought for the first time: Arfon and Dwyfor Meirionnydd replaced Caernarfon and Meirionnydd Nant Conwy, respectively; Aberconwy replaced Conwy. At the time of the election Welsh constituencies had electorates on average around 14,000 smaller than their counterparts in England. Scotland saw its most recent large-scale review completed in 2004, so its 59 constituencies remained the same as at the 2005 general election. Contesting parties Main parties All three main