Boris Johnson could lose more than 100 seats at the next general election, a poll has suggested, with support for the Conservative party falling in the “Red Wall”.

A survey of the 57 Labour heartland constituencies in the Midlands and North gained by the Tories in 2019 found that 38 per cent believed Sir Keir Starmer, the Labour leader, would make the best prime minister. Thirty-three per cent backed Mr Johnson.

Almost half of respondents – 49 per cent – said they would vote for Labour if there was a general election now, while one third would vote for the Tories. Nationally, Labour is ahead in the polls by five points, on 40 per cent of the vote share compared to the Conservatives’ 35 per cent.

Deltapoll, which conducted the research for the Mail on Sunday, said that if the results were translated into seats Mr Johnson could lose more than 100, wiping out his majority and offering Sir Keir the keys to Number 10.