Changing Biases in the Operation of the UK's Electoral System, 1950–97
| Published date | 01 June 1999 |
| Author | Iain MacAllister,David Rossiter,Helena Tunstall,Charles Pattie,Ron Johnston,Danny Dorling |
| DOI | 10.1111/1467-856X.00008 |
| Date | 01 June 1999 |
| Subject Matter | Article |
© Political Studies Association 1999. Published by Blackwell Publishers, 108 Cowley Road, Oxford OX4 1JF and
350 Main Street, Malden, MA 02148, USA 133
British Journal of Politics and International Relations,
Vol. 1, No. 2, June 1999, pp. 133–164
Changing biases in the operation of the
UK’s electoral system, 1950–97
DAVID ROSSITER, RON JOHNSTON, CHARLES PATTIE,
DANNY DORLING, IAIN MACALLISTER and
HELENA TUNSTALL
Abstract
The biased outcomes of recent British general elections, whereby the two main parties
(Conservative and Labour) would have achieved different percentages of the seats in the
House of Commons for the same percentages of the votes cast, are explored, using a method
of bias decomposition developed by a New Zealand political scientist. Overall, the situation
changed markedly between 1950 and 1997: the biases in the system strongly favoured the
Conservatives in the 1950s and early 1960s, but Labour in 1992 and 1997. Examination
of the seven components of the bias measure shows that most of these moved in Labour’s
favour over the 50-year period, with a major shift between 1992 and 1997 because of the
greater geographical efficiency of the Labour party’s vote at the latter date: reasons for this
are suggested.
The Labour Party won the British general election of 1 May 1997 with
43.3 per cent of the votes but 63.6 per cent of the seats: it was an ‘electoral
landslide’ rather than a ‘popular landslide’. Such a biased outcome
favouring the party with the largest share of the votes is quite common in
plurality electoral systems (see for example, Rae 1971, Lijphart 1994, and
Taagepera and Shugart 1989), but in the United Kingdom it is generally
assumed that the bias favours the Conservative party much more than
Labour: since 1950, when the current system of constituency definition
was introduced, Labour has never won more than 57.6 per cent of the
seats (in 1966), even though it exceeded its 1997 share of the votes cast on
six occasions between 1950 and 1966. To what extent was the 1997 result
different, and why? To answer this, we apply a method of analysing bias
in single-member plurality constituency systems to a study of the UK since
1950, explore variations in the nature and extent of such bias over the
country’s last fourteen general elections and suggest how Labour’s ability
to exploit that bias enabled it to win such a substantial ‘electoral landslide’
in 1997.
Figures 1 and 2 set the context for this exploration by indicating how
markedly the 1997 general election result deviated from the preceding
thirteen.1Figure 1 shows the relationships between the percentage of the
votes cast for, and the percentage of the seats won by, each of the three
political parties which now contest every seat in Great Britain.2Each in-
dicates not only that the 1997 result differed substantially from the general
trend, but that it was the largest residual: 1997 clearly differed significantly
from all of the others in the allocation of seats relative to votes. Labour
obtained by far its largest proportion of the seats, with a share of the votes
that was close to its median percentage across all fourteen elections (Figure
1A). It did very much better than predicted by its vote share, whereas
the Conservatives did very much worse in 1997 than their party’s linear
relationship suggests, with what was by far its lowest share of the votes
cast (Figure 1B). Finally, the Liberal Democrats, like Labour, did very
much better in 1997 than their general trend over the full set of elections
suggests (Figure 1C), getting much their largest share of the seats with a
percentage of the votes cast that had been exceeded on five previous
occasions.
The two sets of percentages in Figure 1 are combined in Figure 2 as
each party’s seats:votes ratio, the ratio of its percentage of the seats to
percentage of the votes (a ratio of 1.0 indicates that a party got the same
percentage of the seats as of the votes, whereas a ratio exceeding 1.0
indicates a greater share of seats than votes). Once again, 1997 stands out,
with Labour and the Liberal Democrats getting their largest ratios by
substantial margins, whereas the Conservatives obtained their lowest. Both
Labour and the Conservatives recorded ratios above 1.0 at nearly every
election (Labour’s fell below 1.0 on three occasions—all in the 1950s: the
Conservatives’ ratio was below parity at only one election prior to 1997—
in 1966, when Labour had a majority over them of 96 seats: Table 1);
apart from the 1951 and 1955 elections, when they fielded very few candi-
dates, the Liberals only once achieved a ratio as high as 0.2 before 1997.
Overall, the pattern is typical of that associated with first-past-the-post
David Rossiter et al.
134 © Political Studies Association 1999.
Changing electoral biases in the UK
© Political Studies Association 1999. 135
Figure 1. The relationship between votes won and seats won (percentages of the total)
1950–97
70
65
60
55
50
45
40
35
30
25
20
65
60
55
50
45
40
35
30
25
20
10
8
6
4
2
0
20 30 40 50 60
Percentage of votes
1997
20 30 40 50 60
Percentage of votes
0 5 10 15 20 25 30
Percentage of votes
B The Conservative party
A The Labour party
C The Liberal Democrat party
1997
1997
Percentage of seatsPercentage of seatsPercentage of seats
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