Cross-party talks to break the Brexit deadlock are "not getting very far", a senior shadow minister has said, dealing a further blow to hopes of a breakthrough.
Jonathan Ashworth, the shadow health secretary, claimed the government was refusing to agree to Labour's demands for a customs union with the EU and accused Theresa May of being "unprepared to compromise".
The comments contradict claims made by those involved in the negotiations, who have repeatedly said that talks have been "constructive" and made progress.
Government ministers have been meeting with senior Labour figures since the start of April in an attempt to find a cross-party solution to the current impasse.
Mr Ashworth told the BBC's Andrew Marr Show: "What we are trying to do is say we want a Brexit deal on a permanent customs union basis, something that secures rights for workers and environmental protections and a single market relationship.
"That is what we have been negotiating with the government - we're not getting far, by the way, but that is the basis of our negotiations."
He added: "We've always said that we accept the result of the referendum, we've put forward our alternatives and we're trying to negotiate that with the government. As I say, it's not getting very far but we're still engaging in those negotiations in good faith."
Asked whether Labour was trying to help deliver Brexit, he said: "We're in negotiations with the prime minister. They're not getting very far but we're trying our best."
The shadow health secretary said Labour had raised the issue of another referendum during the talks but said: "The prime minister isn't prepared to compromise. We have been prepared to compromise and that's been demonstrated by the way we've voted [for second referendum] on three different occasions in the House of Commons."
He urged people to vote Labour in European Parliament elections later this month, saying they were a "two-horse race" between his party and Nigel Farage's Brexit Party in areas where the anti-EU party is performing well.
Current polls suggest that the Brexit Party is on course to win the elections by some way, with Labour in second place.
Mr Ashworth said: "Be in no doubt, if you want to stop Nigel Farage in these elections vote Labour.
"The Lib Dems and Change UK cannot stop the Brexit Party getting MEPs in regions - it's a two-horse race now between Labour and the Brexit Party."
Hopes of the cross-party Brexit talks reaching a positive outcome have faded in recent days after senior figures in both Labour and the Conservatives suggested they were unlikely to succeed.
On Friday, several Labour MPs called on Jeremy Corbyn to pull out of the discussions.
A day later, senior Tory Sir Graham Brady predicted that the talks would "peter out in the next few days without having come to any significant conclusion".
The chair of the 1922 Committee, which represents backbench Conservative MPs, told the BBC's The Week in Westminster that he found it "very hard to see" how the talks "can lead to any sensible resolution".
And former defence secretary Gavin Williamson, who was sacked by Ms May earlier this month after being accused of leaking details of a National Security Council meeting, told the Mail on Sunday that the negotiations with Labour were "politically naive". Mr Williamson, who denies being behind the leak, suggested the prime minister was making "a grave mistake" in trying to strike a deal with Mr Corbyn.
The talks are expected to come to a head on Monday when the conclusions of the working groups set up by the two parties will be brought together.
The government also plans to speak to the EU this week to discuss whether the bloc would accept potential changes to the proposed future EU-UK relationship that have been discussed with Labour.
Downing Street has admitted that striking a deal with Mr Corbyn's party is now Ms May's only chance of getting a Brexit agreement through parliament.
A government source said: “If the Bill had passed we would have left the EU already. And because parliament has made it clear it won’t accept no deal, the only way to leave and deliver on the referendum is with a deal. The government is determined to deliver on the result of the referendum as soon as possible."
Damian Hinds, the education secretary, defended Ms May's handling of Brexit, saying of the talks with Labour: "What's the alternative? We have to find a way through and that means we have to have a majority."
He told Marr: "I think the prime minister has shown the most remarkable tenacity and drive and commitment in seeing through this process, which has been very difficult - hard negotiations with Europe and at the same time having to deal with all the negotiations at home.
"I think she's done a remarkable job and no one should be under any illusion that just changing the person in that position would change the parliamentary reality."
But he admitted that the European Parliament elections on 23 May will be "difficult" for his party, saying that for many people they were "the ultimate protest vote opportunity".
The latest polls suggest the Conservatives are on course to finish fourth in the elections, behind the Brexit Party, Labour and the Liberal Democrats.
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