Labour will hold fresh Brexit talks with the Tories today as hopes fade that they will reach a deal.
Jeremy Corbyn's top team will hold the second day of talks in a row with Theresa May's most trusted ministers.
But Labour sources warned yesterday's three-hour talks - including with her deputy David Lidington - were the "most robust yet" as both sides clashed over a customs union.
And Jeremy Corbyn is set to clash with Theresa May at Prime Minister's Questions from noon as deadlock continues.
The Prime Minister is thought to have offered a temporary customs union between the UK and EU to 2022 - stopping well short of Labour's call for a permanent one.
A Labour source told the Mirror talks were “disappointing and frustrating” given the “hype” over a customs union offer at the weekend.
"It’s the same deal with a bit of glitter on top," the insider fumed.
Brexit: Labour-Tory talks explained as Corbyn and Theresa May face crunch week
A Labour source told The Times: "It is a million miles away from a compromise that could win the support of Labour MPs.
"And [it is] unrealistic in terms of what we were thinking about in terms of our demands."
Labour's John McDonnell and Shadow Brexit Secretary Sir Keir Starmer are among those returning for a second day of high-level talks this evening in the Cabinet Office.
Shadow Business Secretary Rebecca Long-Bailey admitted the talks were "very robust" and said: "We haven't had any movement or agreement on a customs union, certainly not today."
Ms Long-Bailey dampened talk that Labour could demand a second referendum on any Brexit deal.
She added: "We will see what the rest of the week holds.
Theresa May braces to stay in office until SEPTEMBER sparking new Tory revolt
David Cameron 'blows £8,000 on posh hot tub' in chillaxing Tory's latest splurge
"Our policy position has not changed since the last Labour conference, where a public vote was one of many options on the table, certainly to avoid a Tory deal, a bad Tory Brexit or a no-deal situation.
"Certainly we've been exploring the issue of a confirmatory vote in these discussions, but as yet nothing has been agreed."
Labour and the Tories are trying to agree a unified approach to Brexit that can pass the House of Commons.
Labour's key demand is for the UK to enjoy a customs union with the EU, something Theresa May previously said she would not accept.
This would mean we could do away with customs checks on any goods travelling from or to the EU - including across the Irish border. We'd have to stick to the same tariffs system as Brussels, and that would stop us striking out with our own trade deals around the world.
Labour is also demanding "alignment" with the single market, and the adoption of future EU standards on workers' rights and the environment.
And the party wants a "Boris lock" - legislation that ensures these promises can't be unpicked by a future Tory leader once Theresa May resigns.
Meanwhile, scores of Labour MPs want the party to demand a "confirmatory" referendum - allowing any deal that's agreed to go to a public vote. But that's the subject of a major row.
A Downing Street spokesman said last night's meeting was "constructive and detailed."
He added: "The teams have agreed to meet again for follow-up talks on Wednesday afternoon, recognising the need to resolve the current Brexit deadlock in Parliament."
