Appearing to all but concede defeat before Thursday's election, Sunak appealed to Conservative voters, some of whom have been shifting to Nigel Farage's right-wing Reform UK in protest at his Conservative government, to prevent what he called a Labour "super majority."
The Conservatives look set to be kicked out of office after 14 turbulent years, marked by Britain's vote to leave the European Union in 2016 and the cost of living crisis that followed the COVID-19 pandemic and Russia's invasion of Ukraine.
Opinion polls have consistently given Keir Starmer's centre-left Labour Party an around 20-point lead, with support for Reform potentially splitting the centre-right vote and the centrist Liberal Democrats further draining Conservative support.
Opinion polls have Labour's Keir Starmer the odds-on favourite to win the election. (AP PHOTO)
"If there is an unchecked, unaccountable Labour Party in power with a super majority, think what that would mean for everyone," Sunak told voters at a rally.
"Once you've given Labour a blank check, you won't be able to get it back, and that means that your taxes are going up ... it's in their DNA."
Farage, one of Britain's most recognisable and divisive politicians, has spent decades railing against the establishment and the European Union, and has in recent years campaigned for Donald Trump in the United States.
He entered the election in early June - his eighth attempt at winning a seat in the Westminster parliament - vowing to supplant the Conservatives as the main party of the right.
Polls appear to show that Reform's support peaked in the second half of June, shortly before Farage said the West provoked Russia's invasion of Ukraine. Some of his candidates and supporters have been dropped for racist or inappropriate remarks.
Nigel Farage's party Reform UK has gained support from disenchanted Conservative voters. (AP PHOTO)
While Britain's electoral system means Reform may win millions of votes, the party is unlikely to win more than a handful of parliamentary seats. But that could be enough to split the right in many areas and hand victory to Labour.
Reform said on Monday its membership had doubled from 30,000 to 60,000 in a month, and that donations would help it fund an advertising campaign through the last week.
"It is humbling but also very telling that they are prepared to back their faith in Reform UK with hard-earned cash and I thank each and every one of them," Farage said in a statement.
Britain will likely elect a centre-left government as much of Europe swings right, including in France where Marine Le Pen's far-right National Rally won the first round of a parliamentary election.
With polls showing many voters are undecided, Sunak made a final plea for people to limit Labour's power if it gets into government, saying: "I say to every Conservative: don't surrender to Labour, fight for every vote, fight for our values, and fight for our vision of Britain."
Reuters
