Many thousands of jobs will be lost across the country if the UK leaves the EU without a deal, Greg Clark, the business secretary, has warned. Clark, who is one of a cohort of senior ministers expected to leave government if Tory frontrunner Boris Johnson enters Downing Street later this month, urged colleagues in parliament to “strain every sinew” to avoid no deal.

His warning came as peers tabled an amendment to government legislation in the House of Lords that would stop Johnson from shutting parliament down in the autumn to stop MPs blocking no-deal.

And reports suggested that Philip Hammond, the Chancellor – also tipped for the chop when Theresa May leaves as prime minister – could lead a “sit-in” of MPs if the new leader tries to lock them out of the Commons.

The HuffPost website and i newspaper reported that the chancellor has told colleagues that Speaker John Bercow, opposition MPs and Tory rebels might insist on continuing to debate in the chamber even if Johnson asks the Queen to suspend sittings by a mechanism known as prorogation.

Johnson has not ruled out proroguing, despite former prime minister Sir John Major warning that he will launch judicial review proceedings if he does.

However, Bercow’s spokeswoman said he had not been contacted about any “sit-in” plan.

“This is complete news to the speaker – no such proposition has been put to him,” she said.

Clark is one of a clutch of cabinet ministers, alongside Hammond, justice secretary David Gauke and May’s effective deputy David Lidington, who are thought likely to leave government for the backbenches because of Johnson’s insistence that he will not appoint cabinet ministers who are opposed to a no-deal Brexit in any circumstances.

Work and pensions secretary Amber Rudd accepted on Thursday that no deal would have to be “part of the armoury” for negotiations with the EU, in a move apparently designed to preserve her chances of a job in the new administration.

Speaking to Sky News, Clark said it was “hugely important” to negotiate a withdrawal agreement rather than leave the EU without a deal. He said government had a “responsibility to protect people’s livelihoods in this country.” Asked how many jobs could be lost, he replied: “It’s many thousands of jobs. Everyone knows that.” “I think that every person who considers the evidence that companies have given, whether it’s in the automotive sector, whether it’s in the food sector, whether it’s in aerospace, whether it’s in industries up and down the country.

“You know if you become less efficient and your ability to trade is impeded then, of course, losing your competitiveness means that there will be jobs that will be lost.” He added: “When the country voted to leave the EU, of course, there is a requirement to implement that but I think we need to do it in a way that takes full account of the impact on real people’s lives and do everything we can to ensure it doesn’t visit harm on them.” Clark said he would not “trim and chop and change my views” on the dangers of no deal in order to preserve his place in government.

“They are based on the evidence that men and women up and down this country running businesses, working in businesses, have made it crystal clear to me what that means and I will always represent them,” he said.

“A no-deal Brexit would be enormously damaging and I will do everything I can to persuade my colleagues to avoid that and get a good deal.” He warned that it is not entirely in parliament’s hands to avoid no deal, as any withdrawal agreement and any extension of negotiations beyond Oct.31 must be unanimously agreed by the 27 remaining EU states.

Downing Street declined to say whether May agreed with Clark’s assessment that thousands of jobs could be at risk, saying only: “She has been clear that there will be disruption, our job is to minimise that.” A No.10 spokeswoman said: “The prime minister has always been clear that leaving without a deal would be disruptive. That’s one of the reasons she has worked incredibly hard to enable the UK to leave with a deal.” Johnson and Hunt braced for the release of a grilling by the BBC’s Andrew Neil as the Conservative leadership contest begins to draw to a close.

The pair were each to be interviewed for half an hour in a programme to be aired on Friday night.

The Independent