Opponents say this is part of an effort to purge "Blairites" and other critics of leader Jeremy Corbyn from the party, while supporters of the change say it will help a new generation of Labour MPs emerge.
"We think the real people's vote would be a general election". The pair opted not to take hospitality seating, showing their socialist values.
Illustrative: People hold up placards and Union flags as they gather for a demonstration organized by the Campaign Against Anti-Semitism outside the head office of the British opposition Labour Party in central London on April 8, 2018.
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But the exact wording of the motion to be put to a vote at the party's conference on Tuesday states only that "if we can not get a general election, Labour must support all options remaining on the table, including campaigning for a public vote".
Labour MP Clive Lewis also urged Mr Umunna to get behind the party leadership.
He told the Pienaar's Politics show: "We have a Government that can not govern".
"My big worry is that if we go for a referendum which is seen as just a simple re-run we could divide the country again, we could get nearly the same result or if it's slightly different that people demand another referendum".
With talk of a new election swirling after May's "Chequers" plan was all but shredded at an European Union summit last week and chances of a disorderly departure that could damage the economy rising, the opposition party is under pressure to set the Brexit agenda.
Britain's Labour Party shadow Chancellor of the Exchequer, John McDonnell speaks during a fringe meeting during his party's annual conference, in Liverpool, Britain, September 23, 2018. If that does not succeed, then the party should keep all options on the table, including the possibility of a second referendum on a question yet to be determined.
"I am not sure there is life left in Chequers", Morgan, chair of parliament's Treasury Select Committee and a former cabinet minister under May's predecessor, told Sky News.
While saying she will stick to her guns, May might have little chance but to change tack after a party conference where the deep divisions over Europe that have riven her Conservatives for decades will be in plain sight.
Adam told Clive Bull that he was led to believe Jeremy Corbyn "was a major advocacy of supporting the Brexit result", but criticised him for "throwing it out to the party" just six months before the end.
It sparked uproar, with Jewish newspapers accusing Corbyn of posing an "existential threat" to the Jewish community while furious Labour MP Margaret Hodge described her party leader as "racist" and "anti-Semitic". "We very rarely have referendums in this country, the people have decided against my wishes and my union's wishes, but they have decided".