Cross-party talks to find a new Brexit plan are on the brink of collapse after Labour attacked Theresa May for failing to offer “compromise or change”.

The opposition broke the official silence on three days of discussions with the government, accusing the prime minister of refusing “to come forward” with anything new.

The verdict is a hammer blow to Ms May’s hopes of putting a joint proposal to parliament next week, before she seeks a further Brexit delay at Wednesday’s EU summit.

And it suggests the UK will be forced to accept a much longer extension to Article 50, for a year under the proposal put forward by Donald Tusk, the European Council president.

It came amid warnings from EU capitals that Ms May’s proposal to delay departure until 30 June only, without providing a clear route out of the crisis, had raised the risk of a no-deal Brexit.

Strikingly, Downing Street at first declined to make any comment on the talks – having described the previous days’ meetings as “constructive” – or even confirm who had taken part.

A spokesman for Ms May later insisted the government had “made serious proposals” and was “prepared to pursue changes” to her Brexit deal.

Labour’s decision to publicly criticise the government was prompted by a refusal to reopen the “political declaration” for a future trade deal that accompanies the divorce deal.

Instead, the opposition was being asked to agree a memorandum that would sit alongside the binding withdrawal agreement.

Put It To The People march: Best of The Independent’s pictures Show all 24 1 /24 Put It To The People march: Best of The Independent’s pictures Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent Put It To The People march: Best of The Independent’s pictures Put It To The People protest 23 March 2019 Angela Christofilou/The Independent Angela Christofilou/The Independent

Some Tory sources had suggested Ms May was willing to discuss a customs union – a key Labour demand – or even a Final Say referendum on any deal that emerges.

But, speaking after the talks, Keir Starmer, the shadow Brexit secretary, said: “The government isn’t proposing any changes to the deal. In particular, it’s not countenancing any changes to the actual wording of the political declaration.

“Now, obviously, that’s disappointing; compromise requires change. We want the talks to continue and we’ve written in those terms to the government, but we do need change if we’re going to compromise.”

It appeared the government was only willing to say it would not stand in the way of a Commons vote on a further referendum, without pushing the idea.

Responding to Labour’s comments, a Downing Street spokesman said: “We have made serious proposals in talks this week, and are prepared to pursue changes to the political declaration in order to deliver a deal that is acceptable to both sides.

“We are ready to hold further detailed discussions this weekend in order to seek any such changes in the run up to European Council on Wednesday.

“The government is determined to work constructively to deliver the Brexit people voted for, and avoid participation in the European parliamentary elections.”

But Labour’s criticism was echoed by Nicola Sturgeon, the Scottish first minister, who tweeted: “This is similar to when I met PM on Wednesday.

“She wanted to know where we could compromise, but refused to indicate any compromise she might make. It is a bizarre approach from someone who made great play of wanting to find consensus – and has just wasted yet more time.”

Across the channel, EU leaders used similar language to protest that the prime minister’s letter to Mr Tusk had failed to make the case for a further extension to Article 50.

It requires the unanimous agreement of all 27 EU leaders to grant that extension – without which the UK would crash-out of the bloc next Friday.

Mark Rutte, the Dutch prime minister, said: “The plan was that the British would explain what they wanted from the EU. A letter was sent today which, as far as I am concerned, doesn’t answer this request.”

And Bruno Le Maire, the French finance minister, warned: “If we are not able to understand the reason why the UK is asking for an extension, we cannot give a positive answer.”

Stung by Labour’s attack on the state of the talks, No 10 eventually released a statement insisting it was ready to compromise and for further talks over the weekend.

“We have made serious proposals in talks this week, and are prepared to pursue changes to the political declaration in order to deliver a deal that is acceptable to both sides,” a spokesperson said.

Rory Stewart, the prisons minister, dismissed the idea that the talks were close to imploding, arguing “tensions” had always been inevitable.

“In truth, the positions of the two parties are very, very close and, where there is goodwill, it should be possible to get this done – and to get it done quickly,” he told BBC Radio 4.