The European Union looks set to hit Sir Keir Starmer with an ultimatum over his plans to "reset" EU-UK relations.
Sir Keir has promised a "pragmatic, sensible" approach to the relationship to "make Brexit work" but his red lines rule out a return to the single market, the customs union, or freedom of movement.
But the Prime Minister is under pressure to agree to Brussels' calls for a youth mobility deal allowing young people in the EU greater freedom to study and work in the UK and vice versa.
A leaked document seen by Politico says the bloc sees the youth mobility scheme as "an indispensable element" in its negotiations with Britain.
The internal paper describes it as "essential" for the bloc's future relationship with the UK, according to the same publication.
Sir Keir has pushed back on the idea, amid a reported split in his party as Home Secretary is said to oppose such a move while Mayor of London Sadiq Khan and Mayor of Greater Manchester Andy Burham understood to be in favour.
Mark Francois, who chairs the European Research Group of Conservative Brexiteers, told Express.co.uk: "Starmer ‘Remains a Remainer’ - and always will.
"This is all part of his plan to take us back into the EU, inch by inch and without ever offering the British people a say on it.
"He just surrendered to Mauritius over the Chagos Islands and now he’s planning to surrender to the EU over this aspect of free movement as well."
Shadow Home Secretary James Cleverly previously accused Sir Keir of being ready to cave in to the EU and bring back free movement.
Dame Priti Patel said it should come as no surprise Sir Keir was not being straight with Brits about Labour's "real intentions" with the EU.
Supporters have argued a youth mobility scheme is not the same as free movement, with pro-EU campaigners pushing for Sir Keir to give ground.
Mark English, Head of Policy at European Movement UK, told Express.co.uk: "It is time for a grown up discussion, so the government should reconsider its inexplicable hostility to a youth mobility scheme with the EU.
"After all, the UK has youth mobility schemes with 13 other countries - including Australia and Japan - so it makes sense to have one with our nearest neighbours and closest partners.
"Dismissing the idea of reciprocal youth mobility simply means letting down British young people who face all sorts of economic difficulties and have seen their horizons curtailed by Brexit.
"Young people want and deserve the chance to study or work in Europe. The government owes it to them to make sure they get that chance."
A government source told The Times in August that British negotiators need to be prepared to give the EU some of what it wants, suggesing youth mobility is an area where the UK "will need to move".
Meanwhile, the EU appeared to hint it might be willing to compromise on the scheme in comments made by its ambassador to the UK last month.
Pedro Serrano suggested the scheme could allow young people to move freely during a gap year rather than for longer.
He told Times Radio: "If we have a mechanism that allows young British citizens to go out for a gap year, for example, to any - they have a choice of 27 states within the European Union - to do a bit of learning and pay there for their learning while they're there. Why not?"