The Green Party has said it won’t field a candidate in the Richmond Park by-election, calling on their voters to back the Liberal Democrats in their attempt to beat Zac Goldsmith.
They also called on Labour to withdraw their candidate in the election to give Lib Dem candidate Sarah Olney a better chance of defeating Mr Goldsmith, who currently holds a majority of 23,000 votes.
Mr Goldsmith is running as an independent candidate in the December 1 election after quitting the Conservative Party in protest against the Government’s decision to give the green light to a third runway at Heathrow Airport.
Neither the Tories nor Ukip are fielding candidates to stand against Mr Goldsmith, and Nigel Farage has thrown his backing behind the Brexit supporter.
Some Labour MPs have urged their party to follow suit in order to give the Lib Dems a better chance of winning and the Greens have now joined those calls, calling for a "progressive alliance".
Green Party co-leader Jonathan Bartley said: "This is no normal by-election.
"A regressive alliance of the Tories and Ukip are working together to re-install a pro-Brexit MP who just ran a racist campaign to be Mayor of London.
"The decision not to stand has been made because a majority of local party members believe that a win for a non-Conservative-backed candidate would be a blow to the Tories' hard Brexit, and dent their damaging plans for post-referendum Britain.
"Ultimately we think Britain is better off with fewer Conservatives in Parliament but that doesn't mean for a second that we won't be fighting to win local elections in the area in 2018, or that we won't stand in the constituency in future elections.
"Of course we have big policy differences with the Lib Dems - and I joined many others in marching against the coalition government - but they are simply the only chance we have at this moment to narrow the Conservatives' majority.
"I'd now urge Labour to join us in forming a progressive alliance against the forces of Conservatism and narrow-mindedness. Chances like this don't come about very often - so let's use this opportunity to kick back against the Tories."
Additional reporting by the Press Association
