Laurence Fox will run in the race to replace Boris Johnson as the MP for Uxbridge & South Ruislip in West London.
The ex-Prime Minister announced he would resign from the House of Commons in an explosive letter released on Friday ahead of the conclusion of the privileges committee’s Partygate probe.
A by-election will now be held in Uxbridge & South Ruislip in a major electoral test for Rishi Sunak.
Fox, who starred in DS James Hathaway in crime drama Lewis, will run in the seat after the Reclaim Party leader agreed a “mutual cooperation agreement” with Reform UK.
Laurence Fox often appears on GB News
The deal will see the revamped Brexit Party run in Mid Bedfordshire after ex-Culture Secretary Nadine Dorries spectacularly quit as its MP hours before Johnson.
Fox said: “The Reclaim Party and Reform UK offer the only genuine conservative alternative to the electorate, seeking for a smaller state, lower taxes, control of our borders and a full debate over net zero and the contentious ideologies being forced onto our children in schools.”
Reform leader Richard Tice added: “This cooperation enables us to have extra focus on specific by-elections.
“We have been campaigning for some time in Mid Bedfordshire.
Andrew Bridgen was unveiled as the Reclaim Party's first MP today at a press conference with Laurence FoxPA
“Many people feel totally let down by the two main parties that are both variants of socialism: high tax, nanny state, low growth and open borders.
“We stand for low tax, high growth and net zero immigration.”
Fox previously took on London’s Labour Mayor Sadiq Khan in 2021 but lost his deposit by finishing in sixth place and obtaining just 47,634 votes.
Ex-deputy leader Martin Daubney, who was elected as a Brexit Party MEP in 2019, stood in the 2021 North Shropshire by-election but finished in seventh place with only 375 votes.
However, Reclaim was handed a publicity boost last month when North West Leicestershire MP Andrew Bridgen joined the party following his expulsion from the Tories over a social media post comparing COVID-19 vaccines to the Holocaust.
Brexit Party chairman Richard Tice speaks during the BBC seven-way election debate in Cardiff.
Uxbridge & South Ruislip returned Johnson to the Commons in 2019 with a majority of 7,210 votes.
But current opinion polls suggest Labour’s Danny Beales could win the seat, with Electoral Calculus giving the 34-year-old an 80 per cent chance of victory.
Reform UK’s inclusion in the Mid Bedfordshire by-election could prove slightly more fruitful.
Almost 9,000 voters in Mid Bedfordshire voted for Ukip in 2015 and Reform has twice managed to receive more than 1,000 ballots in by-elections held since it dropped its Brexit Party name.
Boris Johnson resigned as an MP with immediate effect on FridayPA
The right-wing party has 11 elected figures in local Government.
Reform also extended an olive branch to Johnson over the weekend with honorary president and GB News presenter Nigel Farage offering to work alongside the ex-Prime Minister to defend their shared Brexit legacy.
An alliance between the two Eurosceptic juggernauts could prove catastrophic for Sunak as the pair continue to connect with a large section of Tory voters and Brexit backers.