LONDON (BLOOMBERG) - Prime Minister Boris Johnson's Conservatives lost a special parliamentary election to the Liberal Democrats in a wealthy district north-west of London that had been a stronghold for the UK's ruling party.
The Lib Dems defied political pundits to win the by-election in the constituency of Chesham and Amersham.
The seat had been held by the Tories since it was created in 1974.
For Mr Johnson, the result is a rare but significant blip on his record as an election winner who led his party in 2019 to its biggest majority in Parliament since Ms Margaret Thatcher was leader.
By-elections are often quirky contests, fought on local issues, and voter swings don't tend to translate into national politics when general elections are called.
Even so, the victory for Lib Dem candidate Sarah Green is a triumph for one of the smaller parties in British politics.
The Lib Dems have not recovered their national popularity since voters punished them in 2015 for spending five years in a coalition government with the Conservatives under Prime Minister David Cameron.
The party was almost wiped out at the general election of that year and has not regained its supporters since.
In Chesham and Amersham, in Buckinghamshire, Lib Dem strategists sought to make headway amid unease among local voters over Conservative proposals for reforming planning laws.
Lib Dem Leader Ed Davey hailed what he called "a huge victory" for his party, after Green won 57 per cent of the vote, overturning the 55 per cent previously won by the Tories.
"The people of Chesham and Amersham have sent a shockwave through British politics," Mr Davey said.
"We were told this seat was too safe and the Tories too strong. This Liberal Democrat win has proved them utterly wrong."
The by-election was called following the death of the MP who held the seat, former minister Cheryl Gillan.