The reduction in the Conservatives’ majority in Old Bexley and Sidcup is a “rejection of Boris Johnson personally” because the Prime Minister is now viewed as a “liability, not an asset” in Tory heartlands, the leader of the Reform UK party has claimed.

Richard Tice, who stood in Thursday’s by-election and secured 6.6 per cent of the vote, said the result showed a collapse in support for the Government ahead of another by-election in two weeks’ time.

The Conservative candidate, Louie French, was returned as the constituency’s new MP following the death of James Brokenshire, a former Northern Ireland secretary, in October. He won 51.3 per cent of the vote, with a majority of 4,478, compared with Mr Brokenshire’s 18,952.

“The British political landscape has changed tonight: confirmed,” Mr Tice told The Telegraph.

“There are now five parties in the British landscape. We’re the only one with a clear message of cutting taxes, cutting unnecessary regulation, and going for high growth.