In a shock result overnight Liberal Democrat candidate Sarah Olney has defeated Conservative candidate Zac Goldsmith in the race for the Richmond Park constituency.
Olney had won 20,502 votes to Goldsmith's 18,638 votes of those counted at around 2am this morning.
Goldsmith, also a failed candidate for the London mayoralty earlier this year, had a 23,000 vote majority going into the by-election, which was triggered by his resignation from the Conservatives following the Theresa May administration's backing for Heathrow airport expansion.
The successful Lib Dem candidate said she now had a mandate from her constituency to vote against Brexit if it came to a vote in the House of Commons.
Olney said in her victory speech that it had shown Richmond Park voters were rejecting the "Ukip vision" in the UK and the US.
"We will defend the Britain we love…the people of Richmond Park have sent a shockwave".
The Labour party lost its deposit by running in the seat.