Boris Johnson would have the smallest constituency majority of any new prime minister in nearly 100 years, were he to make it to Downing Street.
Mr Johnson has a majority of just 5,034 in his seat of Uxbridge & South Ruislip – the equivalent of 10.8% of all votes cast in his seat at the 2017 general election.
No prime minister since 1924 has assumed office with a smaller personal majority.
When Ramsay MacDonald became Labour prime minister in that year, his majority in the constituency of Aberavon was just 3,512.
Mr MacDonald’s majority was the equivalent of 11.2% of all votes cast in his seat – slightly higher than the comparable figure for Mr Johnson in 2017.
When measuring majority in this way – as a proportion of all votes cast – Mr Johnson’s figure of 10.8% is the lowest since Andrew Bonar Law in 1922, whose personal majority was 8.0% when he became PM.
The largest personal majority of any incoming prime minister of the last 100 years is that of Theresa May.
She enjoyed a majority in her seat of Maidenhead of 29,059 – 54.0% – when she moved into 10 Downing Street in 2016.
Mr Johnson also has the smallest majority of all the candidates standing to become Conservative leader.
Michael Gove, MP for Surrey Heath, has the largest (24,943).
Mr Johnson’s majority in Uxbridge & South Ruislip would be overturned by Labour on a swing of 5.4%.
By contrast, a swing of 21.6% would be needed to unseat Michael Gove.