Hammond said he “strongly” supported Tory ex-prime minister Sir John Major’s threats to seek a judicial review if Johnson prorogues parliament to stop a no-deal Brexit.
Johnson, the overwhelming favourite to be crowned the next PM, has refused to rule out suspending the sitting of parliament to stop MPs passing legislation designed to stop no deal.
And he and has committed to taking the UK out of the EU “do or die” on the next Article 50 deadline of October 31.
But Hammond, who has already said MPs would stage a “sit-in” to stop Johnson from proroguing, told Bloomberg TV: “If anybody were to attempt to shut down parliament in order to carry out a course of action which parliament is known to oppose, that would be very serious indeed.
“That would provoke a constitutional crisis.
“And, if we aren’t able to prevent that course of action through parliament, then, certainly, there will be resort to the courts, and I strongly support the position that Sir John Major has taken.”
It came as Business Secretary Greg Clark warned that a no-deal Brexit could lead to the loss of “many thousands” of jobs.
He urged his party to “strain every sinew to avoid that”, with leadership rivals Johnson and Jeremy Hunt both pledging to leave the EU without a deal if they cannot negotiate a better withdrawal agreement than Theresa May.
Hammond and Clark, along with the likes of David Gauke, have used their cabinet positions to be increasingly vocal about the dangers of a no-deal Brexit because they are expecting to be sacked from the government when Johnson takes office due to their pro-EU stances.
They have threatened to vote against Johnson to stop no deal if necessary, although Work and Pensions Secretary Amber Rudd has dropped her opposition to the idea, saying it has to remain in the “armoury” of the next PM.
Clark told Sky News: “It’s evident that if you have the disruption that comes from a no-deal Brexit there will be people that will lose their jobs.
“It’s many thousands of jobs. Everyone knows that.”
Clark cited evidence from businesses when challenged that some are claiming the UK could weather an exit on World Trade Organisation terms.
“I think every person that 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, 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 there will be jobs lost,” he said.
A spokeswoman for May told a Westminster briefing: “The prime minister has always been clear that leaving without a deal would be disruptive.”