British Prime Minister Boris Johnson suffered an embarrassing defeat when his Conservative Party lost a parliamentary by-election on the outskirts of London, just a few miles from his own seat.

Since its creation in 1974, the Conservatives had comfortably held the leafy, affluent Chesham and Amersham constituency, capturing more than 50 per cent of the vote on every occasion.

However, in an astonishing turnaround, the candidate for the Liberal Democrats — a centrist, pro-European Union party — won a majority of 8,028 votes over the Conservative candidate in results announced on Friday morning.

Asked about the huge swing, junior interior minister Kit Malthouse said: "It's tough and disappointing".

"We would have hoped for a better result," he told Sky News.

The Conservative Party last month won a stronghold of Britain’s opposition Labour Party in Hartlepool in northeast England, which Johnson credited in part to delivering Brexit.

But some have said the approach that is attracting traditional Labour voters in northern England has also alienated some of Johnson's base in the Conservatives' own strongholds.

Johnson's parliamentary seat is just ten miles away, in West London.

"(Voters) have been taken for granted, they feel that the Conservative Party isn't listening to them. Many of them are very unhappy with Boris Johnson," Liberal Democrat leader Ed Davey said, referring to Labour and Conservative party colours.

"Everyone's talking about the red wall in the north, they should think about the blue wall in the south"

Plans to build the new High Speed 2 rail link between London and northern England which cuts through the area had provoked much local hostility in Chesham and Amersham, while government proposals to reform planning laws, which critics fear could lead to more development in southern England, had also riled locals.

The election in the Chesham and Amersham constituency was called after the death in April of Cheryl Gillan, who had represented it for Johnson’s Conservatives since 1992. At the last poll in 2019, Gillan won by a majority of 16,223 votes.