Britain’s main opposition Labour Party is set for its biggest ever victory in next month’s general election, winning by a larger margin than in 1997 under former prime minister Tony Blair, opinion pollsters YouGov said.

YouGov’s poll predicted that centre-left Labour would win 422 seats in parliament, giving them a 194-seat majority, while Prime Minister Rishi Sunak’s Conservatives are on course for their lowest total in more than a century.

The Conservatives are expected to be reduced to 140 seats, according to the multilevel regression and post-stratification (MRP) poll which use big data sets and demographic analysis to predict results in individual seats.

YouGov said it would be the biggest collapse in support for the Conservatives since 1906 and its model suggested that the party could be set for “near wipeout” in many areas, including London, the North East, the North West, and Wales.

The poll data was collected before Brexit campaigner Nigel Farage took over the leadership of the rival right-wing Reform Party party on Monday, which analysts say could hit the Conservative vote further.

A previous YouGov MRP poll published in early April – before Sunak surprised political analysts and even some lawmakers by calling a summer election – showed Labour winning 403 seats nationwide if a general election was held then.

A party only needs to win more than 320 seats to secure a majority in parliament.

Opinion polls consistently show Labour, led by Keir Starmer, roughly 20 points ahead of the Conservatives.

The latest YouGov poll also predicted that the pro-independence Scottish National Party, who are on their third leader in just over a year, would lose more than half their seats.

Labour, which has been put of power for 14 years, are seen taking 34 seats in Scotland, giving them the largest number of Scottish seats in Britain’s parliament, YouGov said.

The poll predicted that senior Conservatives including finance minister Jeremy Hunt, defence minister Grant Shapps, the leader of the House of Commons Penny Mordaunt, and prominent Brexiteer Jacob Rees-Mogg could lose their seats.

“I think that there is only a single poll that matters and it’s on election day,” Shapps told radio station LBC when asked about the YouGov poll.

“We’re going out to win this election,” he said.