Theresa May must take the option of a no-deal Brexit "off the table" before Labour will enter into talks with her, Shadow Chancellor John McDonnell has said.
After surviving a vote of no confidence brought by Jeremy Corbyn, Mrs May invited leaders of opposition parties for talks on the way forward on Brexit, ahead of her announcement on her next steps on January 21.
But Mr Corbyn said the prospect of departure from the EU without a deal must be removed before there could be any meaningful talks.
And Mr McDonnell told ITV's Peston show that there is "an overwhelming majority" in Parliament against no deal.
He said: "We've got to get rid of that off the table because it is catastrophic for our economy.
"I honestly believe there is an overwhelming majority in Parliament against a no-deal Brexit.
"The prime minister seems to be working more to satisfy some extreme elements within her own party than looking after the country's interests."
He also said he believes there is a majority in Parliament for Brexit with a "permanent customs union".
Liz Truss, Chief Secretary to the Treasury, told Peston it was "completely ridiculous" for Labour to refuse to hold talks until no deal was off the table.
She said: "The way that the Labour Party are going to avoid no deal is by supporting the deal that Theresa May has worked so hard to come up with over the last few years."
Asked about if it comes down to a choice between no deal and a referendum, she said: "I think a referendum would be incredibly dangerous. This was a major moment for our country on voting to leave the European Union."
Mrs May said she was "disappointed" Mr Corbyn had "chosen not to take part" in talks but that "our door remains open".
The PM's official spokesman said that, while Mrs May favoured an orderly withdrawal with an agreement, a no-deal Brexit was not being ruled out.
Mr McDonnell said he believed that following this week's events, which saw Mrs May's Brexit deal suffer a colossal defeat in the House of Commons, Parliament would now take control of the process from the Government.
He told Peston: "I think what will happen now is the Labour Party, along with the other opposition parties, and with other members of Parliament, will take the lead in this now because the Government significantly failed to come up with anything they can get through their own party."
Liberal Democrat leader Sir Vince Cable and the Scottish National Party's Westminster chief Ian Blackford both made clear they would use any discussions with the PM to press the case for a second referendum.