Part 1 of a two-part guest series by Harry Hayfield. Part 2 can be found here.

Exit polls came to fame in 1952 when following a long study of the American electorate, NBC fed the information into a computer and after a few moments said “Eisenhower to win”. As the results came in, the computer was proven right and the sceptics wrong.

In our elections, exit polls have only really been around since 1970 when the BBC commissioned a poll of the electors of the “typical” seat of Gravesend. Since 1987 they’ve been a common occurrence, but have they always been as accurate as they were in 2005?

The 1987 election was preceded by a campaign that seemed to suggest that the Conservatives were heading for another landslide victory. However on Election Night, the BBC published a Gallup exit poll that seemed to suggest that everyone else had got it horrendously wrong. They were projecting a national vote share of Con 40%, Lab 35%, Alliance 23%, which suggested a House of Commons comprising 338 Conservative MP’s, 261 Labour, the Alliance on 26 and the Others getting 25.

Given a 2% margin of error, the figures could have reflected a Conservative majority of 86, or a hung parliament with the Conservatives 17 short of a majority. But the BBC stuck to their guns and said “Con majority of 26” as their exit poll forecast. So now all that was needed was a seat to confirm this forecast and in 1987, that seat was Torbay.

Torbay in 1983, like much of the South West of England, had elected a Conservative MP, with the Alliance they were in second place and Labour’s deposit in danger. With the Alliance just 13% behind against an incumbent who was retiring, they were optimistic in 1987. But what was the exit poll suggesting? Con 26,000 votes said Professor Tony King, but when the returning officer made her statement everyone was in for a real surprise!

Not only did the Conservatives hold Torbay, but beat the exit poll into a cocked hat polling 54% of the vote (+1% on 1983). More importantly for the House of Commons forecast, Labour only polled 8% (also +1% on 1983), in other words a negligible swing from Con to Lab: and the effect on the forecast was instantly evident. Instead of 338 Con MPs, the new forecast said 348, instead of 261 Lab MP’s, the new forecast said 252, the Alliance remained on 26 and the Others fell to 24. And so it carried on all evening. As the Conservatives held seats that the exit poll suggested would fall to Labour, the forecast majority continued to climb to the final result of 102.

Ten years later in 1997, battered and bruised from their failed 1992 forecast, the pollsters made sure that they weren’t going to make the same mistake again and completely rejigged their methods to include “the spiral of silence”. This was a theory that supporters of a party that was deemed very unpopular would declare themselves as “don’t knows” or even suggest that they supported another party altogether. So when the BBC election programme started with the exit poll all loaded up and ready for broadcast everyone crossed their fingers and hoped for the best.

“There it is, ten o’clock and we say that Tony Blair is to be Prime Minister and a landslide is likely”

Would those words come back to haunt the BBC at the end of election night? Well, remember that margin of error back in 1987? Well, there was also a margin of error on this poll as well and as in 1987 was also 2%, but there was no way even this margin of error could produce a wrong result surely?

Labour 47%, Conservatives 29%, Liberal Democrats 18% (range 16% – 20%). Whichever way you looked at it, it seemed to be suggesting one thing and one thing alone. A massive rejection of the Conservatives and no poll hiccup! And this was confirmed not only by the first Labour gain (Birmingham, Edgbaston) but the second (Portsmouth North) and even the third gain (Crosby), so it looked as though the pollsters had finally perfected the art of polling as Labour did indeed glide into government with the biggest Labour majority ever of 179.

Next week: the 2001 and 2005 elections

Harry Hayfield is a Lib Dem activist in Wales.