19 January 2015

Former Prime Ministers – some statistics

What uncertain times these are. In the Independent on Sunday on 18 January, Iain Dale, political commentator and former Conservative politician, provided his prediction of the outcome of the May general election (his website is the primary source). It was based on a painstaking consideration of the circumstances of each of the 650 constituencies in the UK parliament, after drawing together whatever local knowledge, polling evidence and so on that he could find. This approach had served Dale well “when I got the European election results bang on and made the most accurate predictions in Cameron’s Cabinet reshuffle”. On the same day in the Sunday Times, Peter Kellner, political commentator, president of the pollster YouGov and husband of a Labour politician provided his forecast (now on YouGov). Their data is in the table below, my additions in italics:

Of course, both men may choose to revise their forecasts in the coming weeks and who knows how robust such predictions would be in the event of, say, a terrorist outrage days before the election. But in both neither of the two main parties is expected to achieve an overall majority, which would suggest that some form of coalition is likely. However, according to Kellner, David Cameron will be leader of the largest party whereas Dale implies that  Ed Miliband, the leader of the Labour party, will be Prime Minister and heading the coalition.

So we may have four former Prime Ministers, with Cameron joining John Major, Tony Blair and Gordon Brown. Or perhaps there will still be three at the end of May. This set me thinking about the number of ex-PMs over the years, hence the chart on the left from 1870 to the current day.

It turns out that for most of the last 100 years, the presence of three or four ex-PMs has been the norm. There only being one, as was mostly the case from 1945-55, was unusual. Only in Gladstone’s final administration was there none, for four years following Disraeli’s death in 1881.  Prime Ministers tend to be long-lived – only one born since 1800 died under 70, Bonar Law, who died soon after leaving office in 1923. The only PM to die in office was Campbell-Bannerman in 1908 at the age of 71.

The mean age at death of the 21 deceased PMs born since 1800 has been just over 81 years, but for the five born and deceased since 1900, just over 88. The latter include one woman, Margaret Thatcher, who died at 87, bringing the average down, contrary to actuarial expectation. Presumably to get the job at all requires a good constitution, but comparison should be made with the life expectancy of upper middle class males (mostly) over 40, not males in general at birth.

On average PMs have lived for 14.8 years after leaving office for the last time (Wilson, Churchill, and Baldwin are among those who returned to office). This becomes 17.2 years if Campbell-Bannerman (see above) and Chamberlain and Bonar Law, who both died within six months of leaving office, are excluded. (The arrows are for Major, above Blair, both to the left of Brown, all on-going of course).

The longest lived was Rosebery – more correctly Archibald Primrose, 5th Earl of Rosebery, probably the most interesting PM statistically. At 45 he was the youngest person to become PM until Blair and later Cameron. His period in office was only 15 months and his estate is thought to have been the largest –so far. The younger they enter office, as has increasingly been the case, the younger PMs will be when they leave:

As far as the next election is concerned, there would be nothing surprising about either outcome as PM in terms of the consequent number of ex-PMs.  However, it seems very likely that the number will go up over the decades ahead. As the table below shows, despite the impression of premierships having become longer, over successive three decade periods, there have been about the same number of office-holders:

However, if the leaving PMs are getting younger and they live to about 90, there will, before long – probably the late 2020s, be six or even seven ex-PMs to be invited to lunch or dinner with the sovereign!


1. Dates of birth, death and office are from Wikipedia.
2. The “quick and dirty” method for dates before 1900 in Excel was used.
3. Photograph at top, 1985: PM Thatcher, ex-PMs Callaghan, Douglas Home, Macmillan, Wilson, Heath (left to right).
4. Second photograph, 2012: PM Cameron, ex-PMs Major, Blair, Brown (left to right), Thatcher was too ill to attend.
5.  Any errors will be corrected if provided as comments.


  1. Well, as in note 5 you solicit corrections: amend the first reference to Rosebery to spell his name in the same way as in the next line. Also, in the Dale-Kellner list, 5 Sinn Fein MPs are predicted, but below this figure 'majority minus SF' seems to deduct only 3 SF MPs. Apologies for such nitpicking, although now I've started a comment I can add how interesting I found this post, which - as in other blog postings - deftly and lucidly presents WI's statistical researches. (David Martin)

  2. Not for the first time – and hopefully not for the last – thank you for your helpful comments. I have corrected Rosebery. As far as the Dale/Kellner figures are concerned, it’s a bit more complicated than just a typo, though there were some in the original table. The removal of 5 Sinn Fein MPs brings the Commons down to 645, so an arithmetical majority is 323, 3 less than in a full House of 650 when it would be 326. Dale seems to have tweaked his figures slightly so I have adjusted them and also filled out Kellner’s which have now been made available on YouGov.