Labour’s David Skaith celebrated as he won the York and North Yorkshire mayoral election on Rishi Sunak’s doorstep.
The area contains the prime minister’s own constituency of Richmond and was previously considered a Conservative stronghold.
It came as another blow to Mr Sunak as the Tories were set to be hit with a humiliating defeat in this year’s local elections.
Mr Skaithe was elected as the region’s first leader with 35.1 per cent of the vote, compared with the Tory candidate’s 27.3 per cent.