It is based on the result of smaller polls conducted outside polling stations throughout the day, with interviewers employed by polling companies asking a random sample of voters how they have just voted.
If the exit poll is true the Conservatives would be 12 seats short of an overall majority, on 314, with 266 for Labour, 34 for the SNP, and 14 for the Lib Dems.
Solomon Curtis, Labour candidate in Brighton Pavilion, tweeted: “Hung Parliament! Let’s see what happens. Huge well done to all Labour activists!”
Chris Jerrey, Green Party candidate in Mid Sussex, added: “Exit polls predict a weak and unstable government to take on Brexit. Good! Now they might start to listen.”
James Smith, Something New candidate in Horsham, tweeted: “Theresa May, even if she scrapes it in, is utterly done for. They’ll have the knives out already.”