Rishi Sunak would suffer a heavy defeat at the hands of Keir Starmer if a general election were to take place immediately, a polling company has said.
Sunak won the Tory leadership race on Monday to officially become the UK's next prime minister.
But despite being more popular among voters than his predecessor, Sunak trails Labour leader Starmer in the polls.
According to a modelling sample of 12,000 people by YouGov, Starmer would win 389 constituencies, and Sunak just 127 constituencies. In 116 constituencies voters would not be sure of who to choose between the two.
That would be a huge reversal of the 2019 election, in which Boris Johnson lead the Conservatives to an 80-seat majority.
Support for Starmer over Sunak is particularly strong in both Scotland and Wales, with the new Tory leader failing to win a single seat north of the border.
Sunak told supporters on Monday that the Tory party must "unite or die" after the recent wave of controversy and infighting.
Watch: Brits hopeful Sunak can deliver stability as PM
In a speech at Conservative Party headquarters, he said: "We now need stability and unity and I will make it my utmost priority to bring our party and our country together.”
Sunak won the race to become Britain's new PM on Monday after rivals Penny Mordaunt and Johnson pulled out of the contest.
The modelling shows the scale of the challenge now facing Sunak and suggests he would not triumph in a single one of the 50 constituencies that form part of YouGov’s ‘Red Wall’ definition.
Similarly, Sunak starts his premiership in a bad position relative to Starmer in the ‘Blue Wall’, winning in just ten.
The data revealed that while the former Chancellor just about leads in Harrow East (+4) and Ruislip, Northwood, and Pinner (+3), Starmer is the victor in 43 of the 53 seats, including strong leads in ‘true blue’ constituencies such as South Cambridgeshire (+13), Winchester (+9), and Wycombe (+8).
Additional polling suggests that the majority of people are disappointed Sunak is the new PM with only half of Tory voters pleased.
According to the first YouGov survey taken after Sunak's victory, just 38% of people said they were "pleased or very pleased" while 41% said they were "fairly or very disappointed".
Among Tory voters, Sunak fared slightly better, with 52% pleased and 38% disappointed.
However, Sunak's supporters will be buoyed by any comparison to Liz Truss who performed significantly worse shortly after being named PM.
In that poll, only 22% of the British public were pleased with the new prime minister and 50% disappointed.
On Tuesday, Sunak met with the King before returning to Downing Street where he told reporters the country was "facing a profound economic crisis" and there were "difficult decisions" to come.
But he pledged to approach the problems with "compassion" and "to place economic stability and confidence at the heart of this government's agenda".
In the televised speech, his first official one since becoming PM, he said: "The government I lead will not leave the next generation, your children and grandchildren, with a debt to settle that we were too weak to pay ourselves."