If you are progressive and believe in Britain’s future in Europe, you should vote Labour, right?

Well, actually, no. Jeremy Corbyn’s ambivalence about Europe was well established, even before he declared that Britain could be better off after Brexit. He refused to share a platform with the Liberal Democrat leader Tim Farron during the referendum campaign to make the progressive case for Remain (worker rights, environmental protection, jobs in the single market) – with disastrous consequences. The Remain campaign was dominated by divisive Conservatives, who left many cold in non-Tory areas. When George Osborne warned voters in the North of England not to put their prosperity at risk, some voters quite understandably responded: “What prosperity? I have nothing to lose. And why would I trust you?”

Sir Keir Starmer, Labour’s Brexit spokesman, has been billed as the great hope for Labour’s pro-European faction. But lately even he has given up on membership of the single market. Last month he said:

"This is not to pretend that arguing for changes to freedom of movement will not make a deal on single market access harder. It will. But in the negotiations to come, it is incumbent on the government to fight for the fullest possible market access and reasonable management of migration."

How, fundamentally, does this position differ from the position of Liam Fox, Brexiteer-in-chief?

Even many decent, pro-European Labour MPs feel unable to make the case for a soft Brexit – which would leave Britain in the world’s most lucrative market – because they fear this will be incompatible with cutting immigration. Labour is now effectively two parties. One is anti-immigration, rooted in the regions, and fearful of Ukip doing to Labour what the SNP did to them in Scotland. The other is metropolitan, pro-immigration and fearful of a Lib Dem revival in London and other cities (though curiously in the shape of the Labour party leader, also anti-single market until recently).

Yet there is, as Jackie Ashley and other traditionally pro-Labour commentators have now noticed, a united, pro-European, progressive party proving it can beat the Tories. I refer, of course, to my party, the Liberal Democrats.

It is important to underline that we accept the result of the referendum. This is not about trying to ignore such a massive popular vote, however close. But it IS about fighting fiercely the utter chaos unleashed by the Conservative Brexit government. We can, unashamedly, make the positive case for Britain retaining a close relationship with Europe: because our jobs, worker rights, environment, and cash-starved regions all depend on it.

Our by-election victory in Richmond Park showed that many people are fearful of hard Brexit. While the result was mainly a rejection of the economic uncertainty caused by the Conservative Brexit government, it was also a rejection of Labour’s anti-Europeanism. On the eve of the “Brexit by-election”, Labour claimed 1,600 local party members - this turned out to be rather more than the number of votes cast for their candidate.

I am not claiming Richmond Park is a typical constituency, and that we can expect similar swings to the Lib Dems across the country. But the recent revival of the Lib Dems – record gains in council by-elections, the highest membership this century, a modest opinion poll rise – suggests there is opportunity for an unashamedly pro-European party.

Tony Blair identified how the 20th century became the Conservative century due to the division between socialism and liberalism. Sadly, he was better at identifying the problem than finding a solution, and progressives are arguably further than ever from a breakthrough. Just as Labour did not stand down for us in Richmond Park, we will not stand down for Labour in Copeland. Indeed we have just selected our candidate Rebecca Hanson – who grew up in a deprived area of Newcastle and went on to study at Cambridge and become a lecturer and careers’ adviser. The kind of person, in short, who any progressive should support.

Instead, she will be fighting a Labour opponent in a seat the Tories will hope to gain. But ultimately we will not help progressive politics if we stand aside for Corbyn’s Labour, which would merely give the left false hope that someone of the hard left could become Prime Minister. To us, a Eurosceptic statist such as Corbyn is not even progressive. By doing well ourselves, the Lib Dems will strengthen the hand of Labour moderates to seize back control of their party, or else leave it entirely. Only then will re-alignment be back on the agenda.

Brexit changes everything. So, whatever you thought of the Coalition or the Lib Dems, think again: if you are a progressive, you need Europe – and the Lib Dems are the only party fighting for your European future.

Tom Brake is the Liberal Democrat MP for Carshalton and Wallington and the party's spokesman on foreign affairs.