The shadow chancellor, John McDonnell, has said there are “different views” in Labour about the timing of a general election and acknowledged concerns among his party’s MPs about trusting Boris Johnson.

Jeremy Corbyn is set to meet opposition leaders again on Thursday to discuss when the parties could support Johnson’s call for an election – which MPs refused to grant in the Commons on Wednesday.

“The problem that we have got is that we cannot at the moment have any confidence in Boris Johnson abiding by any commitment or deal that we could construct,” he told BBC Radio 4’s Today.

“That’s the truth of it. So, we are now consulting about whether it’s better to go long, therefore, rather than to go short.”

McDonnell said Johnson was “demeaning the office of prime minister” by suggesting it was cowardice that was preventing an election. “I wish he would put aside Donald Trump’s script for a time and have a serious discussion,” he said.

“We want a general election as well but we want it in the interests of the country when we have prevented a no-deal Brexit, and on that basis we have got to determine the date.”

McDonnell said the party was consulting over the next few days about when the best time to hold the election would be.

“We’re looking now at taking legal advice on how secure that bill is, but we’re also consulting the other opposition parties, and our own party on the date of a general election,” he said.

Senior Labour figures, including Keir Starmer, have suggested that the election should not take place until the extension to Brexit has actually been secured, to ensure Johnson cannot repeal the legislation against no deal.

Multiple Labour MPs have insisted the party must not back any election until after 31 October so that Johnson is forced to request the extension – a move the prime minister has repeatedly insisted he will not do.

The Labour MP Tonia Antoniazzi said on Twitter that a general election must be called after 31 October because “this PM is a Liar and the the UK will not be taken for fools”.

Ben Bradshaw, a former Labour cabinet minister, said Johnson’s call for an election was a “last desperate throw of dice” from which Labour should not rescue him.

“Labour and the other opposition parties must not save him, but ensure an election is only called after 31 October, when he will have failed completely,” he said.

The shadow Foreign Office minister, Helen Goodman, said Johnson was “trying with his friends in the press to bully us into agreeing an election at a time which is not in the national interest”.