General Election 2024: How accurate are exit polls and when are they published?

Words by Connor Parker

After tens of millions of ballots are cast on the day, the first big moment of election night is the exit poll published at 10pm exactly, traditionally giving the clearest indication yet of who will be prime minister in the morning.

Polls are closely followed during election campaigns with experts pouring over them to judge their accuracy, and politicians changing their strategies to reflect them.

But the most accurate of them all is the exit poll which is published after every vote has been cast.

While unable to have any impact on the campaign, the exit poll remains one of the highlights of every General Election.

How ITV News has presented exit polls in the past

How does it work? 

The main reason exit polls are viewed as accurate is because it is conducted after people have cast their vote.

In the UK, more than 20,000 people are selected at random at 133 locations and asked to replicate who they voted for.

The poll is carried out roughly in the same location each time, meaning it provides a good idea of the electoral picture at a local level.

All that data - constituency by constituency - is analysed to give us the national exit poll prediction of how many MPs each party is forecast to gain in the new parliament. 

This year, for the first time since 2010, there have been changes to the boundaries - where constituency maps are redrawn - making the exit poll work even harder.

ITV News election analysts have calculated the boundary changes favour the Conservatives slightly which makes Labour's job a bit harder.

 ITV News election analyst professor Colin Rallings gives his insight on exit pollsThe moment Big Ben strikes ten on the evening of July 4, ITV News will reveal the result of the joint broadcasters' exit poll, forecasting the outcome of the general election.  

ITN has been commissioning exit polls since 1974, and since 2005 the polls have been conducted jointly with the BBC; in 2010 Sky News joined the consortium. 

This year field workers from pollsters Ipsos will be present at more than 130 polling stations across Great Britain, as voters emerge from having cast their ballots.

Those polling stations are chosen to be, as far as possible, the same ones as used at previous elections to facilitate the comparison of results.   

Exit polls do not try to engage with every voter. Rather one voter out of a given number (i.e. one in ten, one in twelve or whatever) is approached. That given number, or sampling fraction, is determined in advance based on a judgment of the likely level of overall turnout.

There are two key ways in which an exit poll differs from a conventional opinion poll. First, it only engages with people who have voted rather than asking about someone’s voting 'intention'.  

Second, respondents are asked to complete a replica of the ballot paper they have just cast in the same secrecy as in the polling booth and to deposit it in a box.

In that way, the confidentiality of the vote is respected, and any danger of responses being constrained by interaction with an interviewer is eliminated.  

The replica ballots are then collated at each polling station and the numbers relayed to the exit poll team working at a secret location in London.

There the returns are analysed to examine what seems to be happening and to have changed since last time, in different types of parliamentary constituency.

Factors which now come into play include party competition, marginality, nation or region, and the demography of the local area by age, education, ethnic make-up etc.

Since 2016, the degree to which electors in an area supported Brexit has also been an important variable.  

Statistical modelling is then used to estimate the probability of one party or another winning a particular seat. In some cases, the result is clear cut; in others, it can look too close to call.  

This having been done for each constituency, the probabilities are added up to produce a final forecast for the country as a whole. 

Although the exit poll has a good record in recent years, it is - like any statistical exercise - subject to a margin of error.  

If the election result is decisive, this will matter less. In a close-run race, the precise outcome could differ somewhat from the initial exit poll.  

It would be disappointing though if the exit poll does not provide a guide to the direction of travel through the night and an indication of where we might end up when all 650 constituencies have declared.

Have you heard our new podcast Talking Politics? Every day in the run-up to the election Tom, Robert and Anushka dig into the biggest issues dominating the political agenda…

How accurate have exit polls been in the past?

The accuracy of exit polls seems to have improved over time. In 1974, the first British exit poll predicted a Labour majority of 132, but the actual majority was three. 

One of the worst misfires was in 1992, when two separate exit polls, for the BBC and ITN, both predicted a hung Parliament.

Instead, John Major's Conservative government held its position, albeit with a significantly reduced majority. 

The 2015 exit poll surprised many by showing the Conservatives far ahead of the polling in the run-up to the vote itself.

Labour had been neck and neck with the Tories during the campaign, with Ed Milliband sometimes pulling ahead of David Cameron.

When the exit poll was published, there was shock as the Conservatives were shown to be in touching distance of an outright majority.

The predicted decimation of the Liberal Democrats was such a shock to former leader Paddy Ashdown that he said he would eat his own hat if it was accurate. His party ended up doing worse than the poll predicted.

In the end, the Conservatives secured a slim majority rather than falling just short of one like the poll predicted.

In 2017, the first take of the exit poll correctly predicted the Conservatives would be the largest party, but stopped short of saying there would be a hung Parliament.

This exit poll was closer to the pre-election polling that had shown a rapid narrowing of the gap between Theresa May and Jeremy Corbyn in the final half of the campaign.

In 2019, the exit poll predicted a Conservative majority of 86 seats, which was very close to the final 80-seat margin of victory. 

What will ITV News' election coverage look like?

ITV’s election night programme, Election 2024 Live: The Results, will be anchored by Tom Bradby, who lead the channel’s coverage in 2015, 2017, and 2019.

Tom will be joined in the studio throughout the night by an unrivalled team of political insider guests, including George Osborne, Ed Balls and Nicola Sturgeon.

Also on hand will be ITV News' Robert Peston, Anushka Asthana and Paul Brand plus ITV's leading election analysts Professor Jane Green and Professor Colin Rallings.

The exit poll will be published at 10pm with immediate reaction from ITV News's presenters coming live on air.

ITV News reporters will be on the ground around the UK throughout the night, bringing news from every corner of the country.

At 6am, Good Morning Britain will come on air with Susanna Reid and Ed Balls co-anchoring.

ITV will remain on air from 9.25am with Julie Etchingham leading the coverage.

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