Rishi Sunak has fired the starting gun on a July general election, setting in motion a few frenzied weeks of campaigning before people go to the polls for the first national vote since 2019.
The last stage before that final verdict will be the exit poll, which offers a unique window on the outcome – and the 10pm ballot does have an impressive track record.
Prof Sir John Curtice, who leads the team that crunches the numbers broadcast to the nation as the polls close, says that its recent history makes the forecast worthy of close attention.
“The record isn’t perfect, but since 2005 the exit poll has given a pretty good indication of where the result will end up on the night. It also tends to be more accurate than opinion polls carried out before voting happens,” he says.
The exit poll is based on a small sample of voters from around 130 polling stations spread throughout the country.
People at each station are approached at random by fieldworkers, who hand them a replica ballot. The voter then privately fills in the ballot to indicate how they voted and puts it into a box.
“We use these replica ballots to make models that predict how constituencies will have voted,” Prof Curtice says.
“The data we get from those ballots is compared against how people voted at the same polling station at the previous general election.
“Crucially this shows the geography of how people’s votes have changed. From this, we make a series of equations that indicate who is likely to win each constituency. When you add up all these equations you arrive at your final forecast for the whole country,” he explains.
