Jeremy Corbyn's shadow justice secretary has threatened to quit the shadow cabinet should Labour's new leader consider arguing in favour of British exit from the European Union.
Lord Falconer, who was reappointed to his post on Sunday, said the UK "should stay in the EU come what may" and "whatever the result of the negotiations" currently being undertaken by David Cameron.
"If the Labour Party adopts a position which says we might leave the EU and might argue against it, my position would become impossible," he told BBC Radio 4's World at One programme on Tuesday afternoon.
Falconer's unstinting pro-EU stance appears to already be at odds with Corbyn, amid confusion over what the party's official position is.
The Labour leader told his MPs on Monday evening he would not give the prime minister a "a blank cheque" by offering unconditional support for EU membership.
And Labour’s new shadow chancellor, John McDonnell, said today that while Corbyn "wants to remain in Europe", Labour would not "going to give Cameron a free hand".
But the new shadow foreign secretary, Hilary Benn, yesterday said Labour wanted Britain to remain in the EU "in all circumstances".
Today some of Britain's leading trade unions have also warned they would encourage members to leave the EU at the upcoming referendum should the British government trade away workers' rights.
An ICM survey published today indicates 43% of people would vote to stay in the EU while 40% would back British exit.
Former shadow business secretary Chuka Umunna left the shadow cabinet over the weekend and raised concerns that Corbyn was not committed to EU membership.
Umunna made clear in his resignation statement on Sunday that the new Labour leader had not given him sufficient guarantees that he would stick to the current policy of campaigning for an ‘In’ vote.
“It is my view that we should support the UK remaining a member of the EU, notwithstanding the outcome of any renegotiation by the prime minister,” he said.
“I cannot envisage any circumstances where I would be campaigning alongside those who would argue for us to leave. Jeremy has made it clear to me that he does not wholeheartedly share this view.”
The Huffington Post understands that Corbyn told Umunna that it was ‘unlikely but possible’ that he would campaign to quit the EU if Mr Cameron failed to maintain workers’ rights.
“Jeremy has not ruled out campaigning for Brexit and it is simply untrue to claim otherwise,” a source said.
“Jeremy and his team are saying different things to different people in an attempt to keep his Shadow Cabinet happy and his Left backers, who hate the EU, on side.”
When asked directly by The Huffington Post at a Labour hustings in July if he would rule out campaigning for an ‘Out’ vote, Mr Corbyn refused to do so.
He said at the time: “No I wouldn’t rule it out...Because Cameron quite clearly follows an agenda which is about trading away workers’ rights, is about trading away environmental protection, is about trading away much of what is in the social chapter.”