Jeremy Corbyn was warned by Labour party chairman Ian Lavery that he risked going down in history as the leader who split his party if he backed another referendum on Brexit, in an extraordinary outburst during a meeting of the shadow cabinet last week, according to senior party sources.

The Observer has been told that Lavery, who has twice defied the whip and abstained on votes on another referendum, delivered the broadside at Corbyn during a shadow cabinet meeting on Wednesday evening, at which Corbyn updated his frontbench team on talks with the government aimed at ending the Brexit impasse.

According to senior figures, Lavery spoke out at the end of the meeting saying he knew his comments would be leaked but was determined to make his point. “He was very angry and wagged his finger at Jeremy, telling him that if he backed a referendum he would go down in history as the Labour leader who split the party,” said one shadow cabinet member. “Jeremy just sat there.”

The outburst stunned shadow cabinet members who said it would have sparked a full-scale shouting match if MPs had not been called to vote at the very moment he made his intervention. At the same meeting several senior figures, including shadow home secretary Diane Abbott and deputy leader Tom Watson, spoke out in favour of Labour backing a “confirmatory referendum” on any deal agreed by MPs, with remaining in the EU as the alternative on the ballot paper.

Lavery has long argued that another referendum would drive away Labour supporters who voted Leave and damage the party’s chances in future elections. Supporters in the party of a referendum argue, however, that failure to back a second vote, in line with party policy decided at September’s conference, would be seen as a betrayal by most party members and supporters who back remaining in the EU. While Corbyn is known to have reservations about supporting a second referendum, he made clear at the meeting the plan was being put on the table in talks with the government.

Tensions over Labour’s position on a referendum intensified on Saturday as a group of 80 MPs, including Corbyn supporters Clive Lewis and Kate Osamor wrote to the party leader demanding Labour make support for a confirmatory vote its “bottom line” in talks with the government.

The letter said “the only concessions Labour could obtain will be non-binding assurances about the future relationship. Any future Tory prime minister could simply rip up these ‘guarantees’ after Theresa May leaves office, and it is the stated aim of the vast majority of Tory MPs to do precisely this.

“The only way to guarantee jobs, rights and protections – and Labour’s reputation with its membership and the electorate – is to support a confirmatory public vote on any option which is agreed by parliament, which will put additional pressure on the government to hold the early general election the country needs.

“Under the current leadership, Labour is offering a vision of hope that has inspired millions of people. Tory Brexit threatens this, and so does any perceived participation in delivering it. Any compromise deal whichthat is now agreed by parliament will have no legitimacy if it is not confirmed by the public.”

The former Labour foreign secretary Margaret Beckett on Sunday says the way forward should be to agree a long extension to EU membership, during which a deal can be thrashed out and a referendum held. Backing EU council president Donald Tusk’s plan for a one-year flexible extension, under which the UK could leave the EU earlier if it ratified a deal, Beckett said: “There is a new path forward around which parliament and the country can unite in the national interest: Donald Tusk’s proposal for a ‘flextension’ of the Article-50 deadline.

“This would give the government the time it needs to negotiate a new Brexit deal, MPs the time they need to scrutinise it, and – with the eventual approval of parliament - the public the chance to sign off any deal in a confirmatory referendum.”