How accurate is the exit poll?

It's the first big moment of election night eagerly awaited by political pundits, broadcasters and you at home. The first indication of just how well or badly the main parties have done, of how the political landscape in this country is changing, and, crucially, of who will be walking into #10 the following day as Prime Minister. But after six weeks in which we've been frankly up to our eyeballs in surveys, what makes this poll, the exit poll, quite so special? Well, exit polls, First off, are very accurate, sometimes down to a margin of only a few seats. And partly that's down to how they're carried out. Commissioned by the broadcasters Sky News, BBCITV News, carried out by Ipsos UK, they have got interviewers at polling stations around the country, 133 of them this year, mainly chosen because of the battlegrounds you've got there. The party competition and the current and the historic data that's captured at polling stations, along with previous results in those constituencies helps to build up a picture of any changes in voter behaviour and that change in the vote share. That and other data is then pulled over by statisticians and political scientists in a sealed room in London. Ingredients for one of the most accurate projections of the election results. So shall we have a look back at how close it's been in the past, starting with this five years ago, 2019, that of course, in that election, Boris Johnson's majority was just six seats off. And then you can see, look, bit of an upset back in 2015 when the seat numbers suggested a hung parliament. Not quite over the line there. But look at this, David Cameron scraping through with a thin majority. Overall though, it's worth saying it has been very close historically. I want to just show you 2010. Look at this, that's what the exit poll was suggesting. And just look at the eventual results. Bang on. Now, shall we take a look at how it actually works on the ground? It's finally Election Day. You know the drill. You head down to your local polling station. Maybe it's a leisure centre or maybe it's a charge. And here we go. I bet you're lucky to be at one of those 133 polling stations around the country. There might be something else. Hello. Hi, I'm Felixos. If you could replicate how you've just voted inside on there and pop into the ballot box for me. Once you have collected all of your ballot papers, what happens to that data? So the Interior will sit down on a bench somewhere, get all the papers out of the ballot box and read them through on the phone. And that's how we enter the data into our systems and are able to process it and send it over to BBCITV and Sky News teams to analyse electronically. Yes, there are secure pipelines. The data comes through to us. We'll model the change in the vote at each of those polling stations and we'll try and look for patterns in that change. It's presumably very secret. Our phones are taken away from us, there are security guards, so we don't communicate with the outside world at all. We just talk to each other. And so it's a very strange feeling as people are still going to the polls, already having a sense of what the result will be. Secure pipeline, sealed rooms. Sounds quite mysterious, doesn't it? But as we've just heard, there is a science and a finely honed art to all of this. And this year's exit poll might be one of the most anticipated yet.