Parliamentary Constituency Boundary Reviews and Electoral Bias

Not to be cited without the authors ’ consent 1 To many observers, the result of the 2005 United Kingdom general election was a clear exemplar of the disproportionality that characterizes first-past-the post electoral systems. The two leading parties – Labour and Conservative – were separated by only three percentage points in their share of the votes cast in Great Britain (36.1 and 33.2 per cent respectively), but whereas Labour obtained 56.5 per cent of the House of Commons seats the Conservatives got only 31.5 per cent. The Liberal Democrats were similarly disadvantaged – as they have been at all post-war general elections: with 22.6 per cent of the votes nationally they were allocated only 9.9 per cent of the seats. Such disproportionality was not the only consequence of the votes-to-seats translation process, however. There was also clear evidence of bias, suggesting that Labour was much better treated than the Conservatives: one analysis indicated that if they had each won 34.7 per cent of the votes cast, Labour would have won 111 more seats than the Conservative