Members of the Liberal Democrats attend the final day of the Liberal Democrats' 2016 Autumn Conference on September 20, 2016 in Brighton, England | Dan Kitwood/Getty Images Why Brexit may revive Liberal Democrats A prominent Brexiteer and a pro-EU Remainer face off in one of the most intriguing by-elections in years.

RICHMOND, LONDON— It’s the bellwether by-election for post-Brexit Britain.

On December 1, a prominent Brexiteer and a pro-EU Remainer go head-to-head in one of the most intriguing by-elections in years — one that has become a significant opportunity for the forgotten party of British politics, the Liberal Democrats.

Strongly pro-EU but a diminished force since a general election wipeout left them with just 8 MPs in 2015, Lib Dems sense a chance of redemption in well-to-do Richmond Park in southwest London, where some 70 percent of voters backed Remain in the June 23 referendum.

The vote was triggered when Conservative MP Zac Goldsmith resigned to protest the government’s plan to build a third runway at nearby Heathrow Airport. Goldsmith, who is standing as an independent with no Conservative challenger, backed Brexit.

Richmond Park won’t just reveal to what extend the Lib Dems have managed to regroup. It will also put to the test a proposition with major ramifications for the next British general election: Whether in the wake of the referendum voters are ready to shed old loyalties and decide their vote based predominantly on Brexit and all it entails.

‘The UKIP of Remain’

The Lib Dems face a big challenge as they hit the wide, tree-lined streets of wealthy Richmond Park. Goldsmith, who grew up in the area and has been the local MP since 2010, won a 23,000 vote majority at the last general election.

For the incumbent, the campaign is about keeping his word on Heathrow. But the Lib Dem candidate, newcomer Sarah Olney, is also anti-Heathrow expansion, allowing her to swing the debate round to the EU.

A poll by BMG Research last month found that the issue that mattered most to local voters — despite the recent focus on Heathrow and Goldsmith’s record — was Brexit.

In the constituency last week, Olney, a 39-year-old local accountant who only joined the Lib Dems in May 2015, was meeting NHS campaigners in a cafe when news broke that the High Court had ruled Prime Minister Theresa May could not trigger Brexit without the approval of MPs.

“I don’t think they like being called a protest party, but they can occupy that space on Brexit” -- Tom Mludzinski, director of political polling at ComRes

Talk turned to Brexit. Local people were “horrified” by the referendum result, said Kathy Sheldon, a retired hospital administrator.

She checked with Olney which way Goldsmith voted. “He was one of the most pro-Brexit MPs in Parliament,” the Lib Dem candidate said, to general murmurs of disapproval.

“This by-election really will show to what extent the referendum has changed political opinion,” Olney said later that day. “It forced people to have an opinion on Europe … to choose a side.”

Goldsmith’s campaign, meanwhile, contests that there is “hardly a whisker” between him and his Lib Dem opponent on Brexit, pointing to the fact that Olney has accepted the outcome of the referendum.

Nationally, Liberal Democrats are positioning themselves as a home for Remain voters — of all political stripes — alienated by May’s apparent commitment to a "hard" Brexit, and the Labour party’s mixed messages on freedom of movement.

The Lib Dems are pro-free movement and want to retain single market membership. They also want voters to have a say, be it through an election or referendum, on the final Brexit settlement with the EU.

So forthright is their stance, they were dubbed “the UKIP of Remain” by columnist James Forsyth in the Spectator — “a party that appeals to a certain slice of the electorate which regards the EU membership as an identity issue.”

Lib Dems bristle at the comparison, but recognize a kernel of truth in it.

“We think we’ve got the opportunity to begin to appeal to people on Europe: hard versus soft Brexit,” said James Gurling, who sits on the party’s ruling federal executive and chairs its campaigns and communications committee.

“If something remarkable happens in Richmond Park, it will be because of Brexit.”

Progressive alliance?

Hopeful signs for the Lib Dems surfaced in the Witney by-election last month. The party surged from fourth to second place, slashing the Tory majority from 25,155 to 5,702 in David Cameron’s old seat.

Party activists say that card-carrying Tory members, outraged by Brexit, turned out to campaign for them.

“We had a carload of Tories who came down from Yorkshire, who arrived with gifts of cheese for the team, and then went out and canvassed all day,” Lib Dem party president Sal Brinton said. "Brexit was part of it, but it was May’s hard line on Brexit as prime minister that spurred them.”

The party, Gurling said, is prepared for a snap election, which now looks more likely after Thursday's High Court decision which ruled the prime minister must allow parliament a vote before beginning the formal process of withdrawing Britain from the EU.

But the Lib Dems have limited resources and must pick their battles, so they are targeting seats lost in 2015, but also those with high levels of Remain support and an incumbent MP, usually a Conservative, who backed Brexit, Gurling said.

“Because our party is pro-European to our core, there is no value in targeting seats that are strongly for Leave,” he added.

Richmond Park fits the bill perfectly.

The Lib Dems aren't the only ones persuaded that Brexit has changed the rules of play.

Senior Labour figures called on the party not to field a candidate in Richmond Park in order to give the Lib Dems a clear run. They were ignored. The Greens have withdrawn and backed Olney, and the pro-EU campaign group Common Ground has called on all “pro-Europeans” to unite behind one candidate.

“There is a space for a party like the Lib Dems at the moment,” said Tom Mludzinski, director of political polling at ComRes. “I don’t think they like being called a protest party, but they can occupy that space on Brexit.”

However, he is more skeptical about the strategy’s shelf life.

"By the next general election, what role will Brexit play? I can’t see it being about trying to stay in the EU or going back into it … Their podium can’t just be lamenting what’s happened, it needs to be about fixing it too.”

For now, expect Lib Dems to make much of their pro-EU credentials. Beat the odds by winning Richmond Park, and the "UKIP of Remain" will start dreaming of being "the party of the 48 percent."

“There will be some people who vote Tory regardless and some who vote Labour regardless,” says Olney. “But people who feel very strongly about Remain have a home with us.”