Senior Labour figures including the shadow foreign secretary, Emily Thornberry, have urged Jeremy Corbyn to resist Boris Johnson’s calls for a snap election until after Brexit has been delayed.

Corbyn’s spokesman said on Wednesday that Labour would be ready to countenance supporting a general election as soon as the bill drawn up by backbench rebels to block a no-deal Brexit has passed.

“The bill that is going to parliament today needs to pass. It needs to pass all its stages. It needs to go through and have royal assent – and once we’re confident they can’t crash out and no deal is taken off the table for 31 October, we will support a general election,” he said.

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“What we’re trying to prevent is the use of any parliamentary procedure or prerogative powers or arrangements in relation to the date of the election to force through a no-deal Brexit on 31 October.” He added: “We want to have a general election as soon as possible and we believe that is the best way to settle not only this issue, but all the issues facing the country.”

But the Labour leader faced a backlash from MPs concerned that supporting an election before 31 October could open the way for the prime minister to achieve a no-deal Brexit – by altering the polling day, or by winning a majority and repealing the bill.

Thornberry said she would prefer a later date than 15 October. “I personally think that we need to have a general election when we’re going to win it. I’ll wait a couple of weeks. If we can give them a little bit of extra rope … just let them be in power for a few more weeks then people can really see how bad they are,” she told Sky News.

She said her party was “making decisions on an hourly basis” but Corbyn would have the final say. “The thing about Jeremy as leader is he listens to different views, he thinks about it, then he comes to a conclusion. It’s good to kick these things around,” she said.

At a hastily convened meeting of the Parliamentary Labour party (PLP) earlier in the day, many Labour MPs expressed concerns about the fear that Johnson could exploit the election timetable to secure a no-deal Brexit.

One MP said they were reassured by an intervention from the shadow Brexit secretary, Keir Starmer, who suggested Labour should not support an election before the bill has been “implemented”, which they took to mean until an extension to article 50 has been secured.

The legislation is aimed at forcing Johnson to ask the EU27 for an extension, if he has not achieved a renegotiated Brexit deal by 19 October, though he has insisted he would not under any circumstances request such a delay.

Polling day has to be 25 days after parliament is dissolved, so if Labour withheld its support until after the legislation kicks in and an extension has been secured, the general election would not be held until after 31 October.

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Starmer later appeared to make the same point publicly at the dispatch box. The Labour MP Ben Bradshaw asked the shadow Brexit secretary: “Would he reassure me that we will not fall into the trap being set by the PM, and we will not support a general election before not only this bill is enacted, but its provisions, including an extension, have been implemented?”

Starmer replied: “I can confirm we will not be voting with the government tonight, and we will keep the focus on the task in hand, which is to ensure that we do not leave the EU without a deal, and that requires the passing and implementation of this act.”

Another option under consideration by Labour is tabling a vote of no confidence in the government, once the anti no-deal bill has passed. If Johnson lost, it would usher in a 14-day period during which Corbyn could try to assemble a governing majority. If he failed to do so, a general election would be triggered.

One veteran Labour MP said the overwhelming view at the PLP meeting was that Corbyn should reject an election before 31 October. They said: “The one thing we must not do with a thoroughly untrustworthy person such as this prime minister is fight an election on his terms. We wait until after he has gone to the EU and see what he comes back with.”

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Another said there were some Labour MPs who favoured an immediate election. “We should not give them a chance to accuse us of running away,” one said. A third MP said the view that an election should not be held until after 31 October was confined to “the usual suspects”.

But the Norwich South MP, Clive Lewis, of campaign group Love Socialism Hate Brexit, said: “The Tories are on the ropes. It feels at this moment in time that there is still wriggle room and for Boris Johnson, through a multitude of ways, to still ensure that no deal happens, even if that legislation passed. And we’re hearing from No 10 that they may not respect that piece of legislation.

“Well the sensible thing to do will be to say: ‘OK, we’ll have a general election, but we’ll do it after we have got the extension signed and sealed at the European council, in legislation, so that we don’t go out on the 31st – and then we can have our election. And in the meantime, let the Tories stew in their own juices, and implode.”

Corbyn held a meeting with other party leaders on Wednesday morning, telling them he would support a general election but only after the threat of a no-deal Brexit had been removed.

The rebels hope the legislation could pass all its parliamentary stages this week, potentially clearing the way for Labour to support a general election if the government tables another amendment on Monday.

Several senior Labour figures, including the shadow justice secretary, Richard Burgon, spoke at a People’s Assembly rally on Tuesday evening, organised under the slogan: “Stop Boris Johnson! Tories out! We demand a general election now!”