Labour tensions over Brexit threatened to boil over on Thursday as two shadow ministers broke ranks to call for a second referendum, and others hinted they could quit the party unless Jeremy Corbyn’s position changed over the next fortnight.

Clive Lewis, a shadow Treasury minister, warned Corbyn that Labour might never be forgiven and could disappear from UK politics if MPs voted to facilitate a Conservative Brexit deal.

Another shadow minister, Paul Sweeney, also backed a second referendum on the final Brexit deal for the first time on Thursday.

The high-profile pro-EU backbencher Chris Leslie said he was “clinging to hope” that the Conservatives would back a fresh poll in the next fortnight, suggesting that he had lost faith in his own party.

Leslie accused Corbyn of “regressing” from the party’s conference policy to pursue a public vote when other options had been exhausted. “I certainly feel we are being played for fools by the leadership of the Labour party on this particular issue. By now we should have reached the stage of a public vote. Nobody can explain to me seriously ... why we are not at that particular stage right now.”

Leslie is among several backbench MPs rumoured to be considering quitting the party in the coming weeks, as concerns mount not only over the party’s Brexit policy but also how it has dealt with cases of antisemitism.

The shadow minister, a prominent supporter of Corbyn, made his comments at a Love Socialism, Hate Brexit rally promoted by the pro-referendum group Another Europe is Possible.

Lewis, who resigned from the shadow cabinet in 2017 to vote against triggering article 50 but returned to the frontbench last year, said Labour could face electoral annihilation similar to that of the Liberal Democrats after the party entered a coalition with the Tories.

Leslie hinted in the House of Commons chamber on Thursday afternoon that his only reason for holding his fire was the hope more Tory MPs would join the second referendum cause before the next vote on 27 February.

“We have to wait for the payroll government ministers to do the brave thing and resign to counteract for some of those numbers lost on what should be a solid Labour move against this outrageous situation,” he said. “The idea that the Labour party is not together and arguing against this tragedy, this disaster, it is for me entirely heartbreaking.”

In a speech loaded with emotion, Leslie said he believed the political system was “shattered … broken and letting this country down at a crucial time. I believe that it is a moment we needed leadership, but what we are seeing sadly is party political calculations … tragically putting themselves ahead of the national interest.”

More than 10 shadow ministers have suggested privately they could resign if Corbyn did not back a public vote in a fortnight’s time – though the Labour leader is also facing pressure from the other wing of his party too.

Sweeney, the shadow Scotland minister, said he owed it to his pro-remain constituency in Glasgow North East, where people voted 67% in favour of staying in the EU, to support a second referendum.

“This is the first time I’ve been explicit on this issue, I never changed my view but I respected the democratic result of the referendum,” he said. “And we had to try our best as honest brokers to try and come to a compromise parliament could deliver but it is quite clear the Tories are not willing to budge at all on any sort of compromise like a customs union.”

Since parliament overwhelmingly rejected Theresa May’s deal last month, Labour has continued to engage with the government after the Labour leader initially declined a meeting with the prime minister. The pair exchanged letters last week setting out their respective Brexit positions, and senior Labour figures met with ministers on Tuesday.

Lewis said he feared those moves were “going to help to facilitate a Tory Brexit” if discussions continued and that it “will be the Labour party that will pick up the flak for what happens”.

“The ramifications for our party will be severe,” he said.

Tensions in the party have boiled over in recent days, with anger from MPs about the pace of dealing with allegations of antisemitism also coming to the fore, particularly the treatment of Luciana Berger by her local constituency party, according to two sources.

Those complaints prompted the party’s general secretary, Jennie Formby, to release statistics about the complaints on Monday, but MPs have demanded further action.

Berger, who is nine months pregnant, is believed to be one of those MPs closest to quitting the party over frustration at the way the party has handled antisemitism allegations and at the party’s Brexit position. It is understood several MPs have worked hard to convince her to stay.

“If Luciana was to quit over antisemitism, that would make our positions untenable for a lot of us,” one MP said.

MPs are convinced that if some of their number quit the party, the move would not come as a unified moment but instead in stages, prompted by different flashpoints.

“Some were frustrated that May took away their opportunity before December, and they were hoping for an amendment [on Wednesday] that would give them a motive,” one senior Labour source said. “They know they can’t wait much longer.”

One Labour MP who has thought about quitting the party said it would be the wrong time to jump ship: “You need to wait until the actual moment of betrayal if and when Jeremy votes for Brexit or rules out a second referendum.”

He said a small number of colleagues were considering leaving the party imminently, but others were urging them to think again because it would look like an attempt to destabilise Corbyn, rather than a statement that they could not support a party that backed taking the UK out of the EU.

“We have to give him as much time as possible to change his mind and back a people’s vote,” the MP said. “We need the shadow cabinet to put as much pressure on him as possible.”

Ben Bradshaw, a Labour MP who supports the people’s vote campaign, ruled out leaving the party over Brexit. However, he said there would be “uproar and a mass exodus from the party” if there were no second referendum.