The result marks the first time the Greens have won a British parliamentary by-election and signals the frustration of left-leaning voters with Prime Minister Keir Starmer.
Hannah Spencer, who won a historic victory for the Green Party on Thursday, outside a polling station in the Gorton and Denton district outside Manchester.
A parliamentary by-election in Gorton and Denton, outside Manchester, will test support for Britain’s prime minister at a moment of intense political pressure.
The arrest of the British former envoy to Washington, long a key figure in the Labour Party, deepened a scandal that has led to calls for Prime Minister Keir Starmer’s resignation.
Peter Mandelson, left, with Prime Minister Keir Starmer in Washington last year. Mr. Starmer fired Mr. Mandelson after learning of Mr. Mandelson’s friendship with the sex offender Jeffrey Epstein.