Labour leader Jeremy Corbyn must call a vote of no confidence in Theresa May “as soon as possible”, the cross-party People’s Vote campaign has said.
Mr Corbyn has ruled out such a move, which could trigger a general election, until he can be sure of winning it.
But the People’s Vote group wants him to get on with it so he can fulfil his pledge to back a further referendum if he can’t get an election.
The group is also urging the government and the EU to plan for a referendum.
Leading figures from the SNP, the Lib Dems, the Green Party and Plaid Cymru – all parties that back a further referendum – set out their demands at a press conference in London.
They were joined by Labour’s Dame Margaret Beckett and Conservative MP Anna Soubry, leading figures from the pro-referendum wings of their parties.
The MPs argued that a referendum was the only way out of the “chaos” caused by Theresa May’s failure to get her MPs to back her Brexit deal – but they also argue that Brexit will harm the people that voted for it in the 2016 referendum.
Making a direct appeal to her leader, Dame Margaret said: “Jeremy, we are asking that in the days ahead you think very hard about adding your signature to those of the other leaders here today.
“Table a motion of no confidence so that, if you cannot get the general election we want, you can campaign for the People’s Vote that Labour’s members and voters so desperately desire.”
The former foreign secretary also urged the government to begin preparations for a referendum by drafting legislation for one.
And she called on EU leaders to begin discussions at their summit on Thursday to extend Article 50 – the legal mechanism taking the UK out of the EU on 29 March – to give the UK Parliament the “time and space” to explore the option of deciding to stay in.
Lib Dem leader Sir Vince Cable said the UK government was doing plenty of planning for a no-deal Brexit, which it did not want but thought possible, but “no planning appears to be taking place for a people’s vote which we believe is highly probable”.
Time was needed to give Parliament a “proper debate”, he said, and to settle the issue of the question on the ballot paper, which he argued should be a “binary choice” including staying in the EU.
Tory Remainer Anna Soubry said: “The biggest obstacle to a people’s vote at the moment is Jeremy Corbyn. If not now, when Jeremy? He has got to start this process now.”
She said she would vote in support of Mrs May’s government in a no confidence vote – but denied the idea that Mrs May would never back another referendum, noting that the PM had also ruled out calling a general election and then changed her mind.
Plaid Cymru’s leader at Westminster, Liz Saville Roberts, said: “Jeremy Corbyn runs the risk of being seen to condone the chaos for his own possible benefit.”
She suggested the Labour leader might be “more comfortable” with a no-deal Brexit “given the degree he hasn’t fought with passion for the European cause so far”.
Ian Blackford, the SNP’s leader at Westminster, said “I think Jeremy has until the close of business today” to table a no confidence motion – or the other parties would do it.
Any MP can table a vote of no confidence but the main opposition party is the only one likely to be granted the Parliamentary time for a vote on it.
And it would stand very little chance of success without Labour or Conservative backing.
‘Friend and colleague’
Asked if the People’s Vote campaign was setting Mr Corbyn up to fail, given that it was unlikely a confidence vote would pass at this stage, Mr Blackford, said it would be a “lever” to force another referendum.
Green MP Caroline Lucas appealed to Mr Corbyn as a “friend and a colleague” who shared her desire for “radical” change to the country.
“The People’s Vote campaign is not about replacing him as a leader,” she said.
“It’s not about, for Heaven’s sake, another party.
“What is about is tackling together the real problems that affect this country and, right now, are going to be harder to address if we go ahead with Brexit.”
Addressing claims the campaign was undemocratic, she said: “How can the will of the people be undermined by a vote of the people?”