Are UK party leaders typically from safe seats?

Question

In the UK Parliament, the 2015 election results for party leaders going into the 2017 election were:

• Theresa May, Conservative Party, Maidenhead, 65.8%. Next party is Labour Party at 11.9%. Chance of unseating negligible.
• Jeremy Corbyn, Labour Party, Islington North, 60.2%. Next party is the Conservative Party at 17.2%. Chance of unseating negligible.
• Tim Farron, Liberal Democrats, Westmorland and Lonsdale, 51.5%. Next party is the Conservative Party at 33.2%. Chance of unseating slim.
• Caroline Lucas, Green Party of England and Wales, Brighton Pavilion, 41.8%. Next party is Labour at 27.3%.

However, in the Scottish Parliament, the 2016 election results for the Conservative Party leader is actually very marginal: 30.4% for Ruth Davidson, with the second party, SNP, at 28.6%. Chance of unseating significant.

Is there any pattern in which party leaders in UK parliaments are typically from safer seats than average MPs?

Answer 1

I've approached this question by looking at the General Election before each party leader attained their post, for Westminster party leaders of the Lib Dem, Labour, & Conservative parties selected since the 1992 GE. I then look at the distribution of 'percentage majority' among MPs of the same party, and find the percentile in which the leader appeared. After collating these results, I have then tested the null hypothesis that the percentiles come from a uniform distribution - i.e. that majority compared to the rest of one's party has no correlation with election as leader.

For example, to get Boris Johnson's score, I look at the distribution of Conservative MP's percentage majorities in the 2017 General Election. I then find the percentile score of his ~10% majority, approximately 23.3.

The results are below:

               Name    GE  percentile
         Tim Farron  2015    2.155172
      Boris Johnson  2017   23.343849
     Michael Howard  2001   38.554217
    Charles Kennedy  1997   47.826087
  Iain Duncan Smith  2001   48.192771
        Ed Miliband  2010   70.041322
         Tony Blair  1992   70.848708
        Vince Cable  2017   75.000000
        Theresa May  2015   78.879310
      David Cameron  2005   81.818182
         Nick Clegg  2005   83.870968
       Keir Starmer  2019   85.148515
      William Hague  1997   85.454545
         John Smith  1992   88.191882
         Jo Swinson  2017   91.666667
      Jeremy Corbyn  2015   91.810345
       Gordon Brown  2005   92.394366
   Menzies Campbell  2005   96.774194

A Kolmogorov–Smirnov test of these percentiles against a uniform 0-100 distribution gives a p-value of ~ 0.002, so we can reject the hypothesis that 'safe-ness of seat' compared to the rest of one's party has no correlation with selection as party leader. This is illustrated quite nicely by the box-plot below:

These results suggest that party leaders are typically drawn from safe seats. Of course, correlation doesn't necessarily mean causation; MPs could hold large majorities due to their own personal qualities, which also make them successful leadership candidates. Note also that just because a seat is safe compared to the rest of one's party, it doesn't mean that it is safe in general - notably, Jo Swinson had a seat in the 91st percentile of safe-ness compared to her party, but then lost her seat in the 2019 GE.

Answer 2

This is a question which we can attempt to get some figures for. Limiting ourselves to the Conservatives, the Liberal Democrats and the Labour party (since the Greens, the Northern Irish parties and the Nationalists all have broken sequences) the last 6 elected leaders had the following vote shares on accession:

• Conservatives: 65.8% 49.3% 45.0% 48.2% 48.9% 63.6% mean 53.5%

• Labour: 60.2% 47.3% 58.1% 60.5% 61.3% 59.4% mean 57.8%

• Liberal Democrats: 51.5% 51.1% 52.1% 38.7% 51.4% 43.6% mean 48.1%

If we look at the 2010 general election results, we can see that 116 MPs (from 649 excluding the speaker) got a higher vote share than the average Conservative leader, versus 48 for the Labour leader and 277 for the Liberal Democrat leader. So, this paints a fairly compelling narrative that party leaders are more likely to hold a safe seat than your average MP.

On the other hand, looking at the 2010 data, half of MPs were elected with a majority of 20% or more, so it's not like there aren't a lot of safe seats out there.