Jeremy Corbyn has insisted Theresa May must compromise on her Brexit red lines if cross-party talks on EU withdrawal are to succeed.
The Labour leader said it is “scandalous” the Prime Minister did not seek dialogue with Labour on Brexit earlier.
Mr Corbyn said Mrs May should not use the delay of Brexit until October 31 as a chance to put her Withdrawal Agreement to the Commons again.
Referring to the talks between the Government and Labour, Mr Corbyn said: “It’s scandalous that it came so late in the Brexit process, not at the eleventh hour, not even at five to midnight, but at five past midnight after she missed her own deadline of the 29th of March.
“Nevertheless, we’re engaging in the talks in a serious and constructive way.
“But we must see those red lines moving and we must see real compromise.
“And I have to say, it is a challenge to negotiate with a Government that’s collapsing – when you can’t be sure if commitments made by the Prime Minister will survive the week and when Cabinet collective responsibility has given way to collective irresponsibility, with ministers contradicting each other on the airwaves.
“Nearly everyone now agrees that the Prime Minister could and should have tried to build a consensus much earlier.”
Mr Corbyn was scathing about how the Prime Minister had handled Brexit.
Speaking at the Welsh Labour conference, Mr Corbyn said: “Just three weeks ago she said she wasn’t prepared to delay Brexit beyond the 30th of June.
“But now we’re holding European elections, not knowing whether MEPs will take their seats or for how long. It’s extraordinary.
“We cannot remain stuck in this loop for another six months.
“I urge the Prime Minister not to see this extension as another chance to flog her dead deal.”
Mr Corbyn added: “We’ve put forward a sensible alternative plan that would ensure a close economic relationship with the EU after Brexit.
“If it’s not possible, we believe all options should remain on the table including the option of a public vote.”
Meanwhile, a poll by Opinium put Labour seven points ahead of the Tories.
The survey shows Labour climbing one point to 36%, while the Conservatives have dropped six points in two weeks to stand at 29%.
Ukip are up two points to 11%, and the Liberal Democrats have dropped one point to 8%, on the survey.