Sunak said he took responsibility for his party's loss, and that he had called Labour leader Keir Starmer to congratulate him on his victory.
Voters in the U.K. cast their ballots Thursday in a national election to choose the 650 lawmakers who will sit in Parliament for the next five years. With most seats counted, Labour, led by Starmer, has gained at least 400 seats in Parliament.
After more than a decade in power under five different prime ministers, Sunak 's Conservatives are set to have their seats in the 650-seat House of Commons cut down to around 130. That would be the Tories' worst result in the party's two-century history and one that would leave the party in disarray.