BRISTOL, England — The U.K.'s self-confessed Brexit "hard-liners" have rediscovered the art of insurgency.

If the polls are correct, the Liberal Democrats are on course to shake off the taint of five years in a coalition government that stripped their vote to its core and left them with enough MPs to fill a camper van.

Like the Brexit Party led by Nigel Farage — set to be the runaway success story of the country's unexpected European election — the Lib Dems have embraced their place at one extreme of the U.K.’s polarized post-Brexit politics.

Their slogan — “Bollocks to Brexit” — is a case in point.

Unequivocally backing a second referendum and remaining in the EU, without the kind of caveats attached to the larger Labour Party’s Brexit policy, the Lib Dems are free to encapsulate their stance in three simple words.

“We’ve got to cooperate. It’s a necessity. And I will continue to make that argument” — Lib Dems leader Vince Cable

And so far, it appears to be working, with the party climbing steadily in the polls. Activists now whisper excitedly of the prospect of getting more votes than the Conservative Party at a national election for the first time since 1906 — and even overtaking Labour.

POLITICO’s latest projections, based on an aggregation of recent polls, bears that out, putting the party at 16 percent, with 12 seats (up from one MEP), just ahead of the Tories on 10 percent with seven seats. The Brexit Party is out in front with 33 percent (26 seats), with Labour on 17 percent (14 seats).

But things could have been even better if the national parties backing a second referendum and Remain — the Greens and new outfit Change UK — had formed an alliance. It is something that veteran party leader Vince Cable, in a message his successor, who will be appointed this summer, says must happen if the party is to turn a good performance at a European election into success at the next general election.

“I think we have to … it would be foolish for the parties that are basically in the same position politically to be fighting each other,” he told POLITICO. “We’ve got to cooperate. It’s a necessity. And I will continue to make that argument.”

Fragmented Remain vote

Cable, who confirmed that it remains his intention to stand down in the summer to make way for a new leader, made his name as the quintessential serious politician, once dubbed “the politics of substance made flesh.”

So how does he feel about “Bollocks to Brexit”?

“I have looked at the etymology of the expression [“bollocks”] which is from the 18th century. The reference said the word had a ‘long and serious history,’” he said during a campaign visit to Bristol, southwest England. “So I felt rather better about it.”

Last week, the Lib Dems' status as the apparent winners of the contest to be the most popular pro-Remain party appeared to have been sealed when the lead candidate in Scotland for Change UK, the party formed by 11 rebel Labour and Tory MPs, defected to the party. Another of its candidates, Rachel Johnson, who left the Lib Dems to stand for Change UK, said at the weekend she felt like a rat who had jumped on a "sinking ship."

Leaked Change UK strategy documents last month showed the new party’s plan to peel off Lib Dem activists and funders, replacing the party as the main pro-EU option. So with Change UK bumping along at 4 percent in the polls, does Cable feel a certain Schadenfreude?

“There is an element of that ... but the votes haven't been counted yet and I don’t want to go around saying we told you so … We are going to have to try to work together.”

The Lib Dems have struggled to shake off the criticism that in coalition government with the Conservatives from 2010 to 2015, they were co-architects of austerity.

According to POLITICO's projections, the vote of the Lib Dems, the Greens and Change UK combined would amount to 29.5 percent, a share that comes close to rivaling the Brexit Party.

The ambition of Remain parties, said Cable, should be to create a “serious alternative” to what he characterizes as “two potential disasters, a nationalistic Tory government probably hauling Farage on board, or a Corbynite government.”

The new hard-liners

In a new pamphlet — perhaps a valedictory set of lessons for his successor — Cable calls Brexit “a symptom of a deeper political shift involving the politics of identity and the emergence of new alignments that do not fit comfortably into the ‘left-right’ narrative.”

If the European election, dominated by Brexit, is a test-case for what he calls the “new polarity” then the Lib Dems need to be unashamed of their status at one extreme.

“On this issue we are not centrists. We are hard-liners,” he said.

But in a general election, issues other than Brexit will come to the fore. In their battle with Labour in particular, the Lib Dems have struggled to shake off the criticism that in coalition government with the Conservatives from 2010 to 2015, they were co-architects of austerity. They argue the policies were necessary to rescue an economy smashed by the financial crisis. Labour pledges to reverse many of the spending cuts that have angered and exhausted voters.

Cable, who served as business secretary in that government, defends much of what the coalition did as necessary to avert economic calamity. “You can’t and shouldn’t wipe out history. Many of the things we did were good and I’m proud of them,” he said.

“There were some negatives for sure,” he conceded, but rejected the idea that the Lib Dems need to make a clean break with the coalition years. “Where we’re getting to is a combination of insurgency with a credibility that comes from having been in government both local and national,” he said.

Leadership election

The party entered the European election off the back of impressive local election results, in which they gained more than 700 councillors. Should they do well this week, their momentum could carry on into the summer with the election of a new leader.

The favorite is deputy leader Jo Swinson, the 39-year-old MP for East Dunbartonshire in Scotland. Cable is 76 and on his visit to Bristol, joked with a student activist about his senior citizens’ bus pass and being an “old codger.” Swinson gives speeches at anti-Brexit marches carrying her 10-month old son Gabriel in a baby carrier.

Speaking to POLITICO in her Westminster office, she has none of Cable’s polite reservations about uttering the new Lib Dem slogan.

“I’ll say it absolutely: ‘Bollocks,’” she said with gusto. “Maybe it’s because I’m from Glasgow, I don’t know, but it doesn’t strike me as a particularly dreadful word.”

Swinson is slightly more circumspect than Cable about the coalition government, which she too served in, as a junior minister.

“I think there is something to learn [from Brexit]," she said. "There’s too many people who find that things are too hard and a decade of wage stagnation has clearly made that more difficult. My view, with the benefit of hindsight, is that before the financial crash the economy was broken in terms of whether it was working for everybody in society … what we found with the financial crash was that all that difficulty came to the fore."

And she said "those small 'L' liberals on the progressive side of politics," including those in the coalition, did not have a strong enough answer about what needed to change.

"It was a crisis. The economy was collapsing … [but] those who have had a nationalist agenda to push have been able to pour into that situation their view that the problem is the EU, or immigrants."

Swinson is yet to formally declare her intention to run for the leadership, but sets out her stall as one who would be open to the Lib Dems being “open-minded to radical ideas” like, for instance, building on the party’s long-standing environmentalism, by considering a U.K. version of the Green New Deal.

“The time for incrementalist policies is not now. Things are more fundamentally broken,” she said. She rejected the idea that a European election in the time of Brexit is a special case, and that the Lib Dem revival might be a flash in the pan.

“Because it’s such a totemic issue I think it does carry beyond … people will remember where the parties were on Brexit for quite some time,” she predicted.

This article is part of POLITICO’s premium Brexit service for professionals: Brexit Pro. To test our our expert policy coverage of the implications and next steps per industry, email pro@politico.eu for a complimentary trial.