Thursday night’s exit poll put the Conservatives on 314 seats. If this is correct then a combination of Labour (266), the Scottish National party (34) and the Liberal Democrats (14) would have exactly the same number of votes as Theresa May’s party.
A minority Tory government could probably rely on the votes of the 10 or so unionists from Northern Ireland, assuming the latter’s 2015 result is repeated. But a minority Labour-led government (or the “coalition of chaos”, as May called it), could rely on Plaid Cymru (3), the one Green MP and the SDLP (three in the last parliament).
Broadcasters have been using exit polls since at least 1974 and it is true that in the 1970s, 1980s and 1990s there were were some horrific misses. Here are the figures, showing how far the gap was between the predicted majority of the winning party and the actual majority.
October 1974
ITN wrong by 12
BBC wrong by 132
1979
ITN wrong by 20
BBC wrong by 29
1983
ITN wrong by 28
BBC wrong by two
1987
ITN wrong by 34
BBC wrong by 76
1992
ITN wrong by 62
BBC wrong by 70
1997
ITN wrong by 20
BBC wrong by six
But in the last decade and a half the exit polls have become much more accurate.
2001
ITN wrong by eight
BBC wrong by 10
From 2005 onwards there has been a joint exit poll, firstly commissioned for ITN and the BBC, and then, from 2010 onwards, for Sky too. Its record has been much better.
2005
Correct. It predicted a Labour majority of 66, which Labour got.
2010
Correct. It said the Tories would be 19 short of a majority, and they were.
2015
Wrong by 22. It said the Tories would be 10 seats short of a majority, but they got a majority of 12.
This chart, posted on Twitter by the Spectator’s Fraser Nelson, makes the same point:
Why we'll probably know the result at 10pm... https://t.co/jQuNfk9GWo pic.twitter.com/QNkyY7DXh6
— Fraser Nelson (@FraserNelson) June 8, 2017
