Ukip has endorsed Zac Goldsmith, the former Conservative MP who is now standing as an independent in the Richmond Park by-election.
The party’s interim leader, Nigel Farage, said Ukip would not put up a candidate against Goldsmith, who backed Leave in the EU referendum, and its supporters should vote for him to stop the pro-EU Liberal Democrats from winning the seat.
Goldsmith, who was the Conservative candidate for mayor of London in May’s election, resigned as an MP earlier this week after the government’s decision to approve expansion at Heathrow, which he opposes. The Conservatives have said they will not put up their own candidate against Goldsmith.
The LibDems, who held the west London seat until 2010, have high hopes of winning it back, thanks to their opposition to Heathrow expansion and their support for the EU. A large majority of voters in Richmond Park voted to remain on June 23.
Ukip, which came fifth in the seat at last year’s general election, said it respected Goldsmith’s decision to fight Heathrow expansion.
“Goldsmith has resigned on a matter of principle and Ukip admire him for having the courage to do so,” a spokesman said. “Ukip have always believed that Gatwick was a preferred option to Heathrow.
“Recognising Zac as a principled man, who was fully committed to helping get Britain out of the European Union, Ukip leader Nigel Farage, in conjunction with our national executive committee, have agreed that we will not be fielding a candidate in the upcoming by-election for Richmond Park.”
The spokesman said the LibDems were “committed to overturning the result of the 2016 referendum and ignoring the will of the British people. This must not be allowed to happen.”
The LibDem leader, Tim Farron, said the endorsement showed Goldsmith was “the Ukip candidate”.
“Goldsmith claimed Brexit has nothing to do with this by-election,” he said. “The very public endorsement he has picked up from the party of Nigel Farage nails that lie.
“This by-election presents a golden opportunity to defeat one of the leading Brexiteers, who is determined even (to) take Britain out of the single market. He might be able to afford the huge damage this would do to our economy, but many people in Richmond Park are worried about the effect on their jobs and livelihoods as a result of the Conservative government playing Russian roulette with the British economy.
“Goldsmith can get as many hard-right candidates to give him a clear run as he likes: he knows he faces a major battle with a Liberal Democrat party determined to keep Britain open, tolerant and united.”
On Wednesday, the Labour frontbenchers Clive Lewis and Jonathan Reynolds, as well as the former shadow minister Lisa Nandy, suggested their party should not contest the seat, where Labour came third in 2015. The trio said it would be preferable not to split the progressive vote, with the LibDems standing a chance of reducing Theresa May’s majority.