The government will “test to the limit” a new law designed to force it to seek an extension to the Brexit deadline if a deal is not reached by 19 October.
Foreign Secretary Dominic Raab said the government would abide by the law but would “look very carefully” at its “interpretation” of the legislation.
He said Britain remained committed to getting a deal with the EU.
The law, which should gain royal assent on Monday, aims to stop the UK exiting the EU with no deal on 31 October.
Prime Minister Boris Johnson has been warned he could face legal action if he chooses to flout it.
Chancellor Sajid Javid said the government would obey the law but “absolutely will not” ask the EU to extend the date of Brexit, as it sets out.
“Of course this government will obey the law. We are going to continue to work towards exit on 31 October. We will leave on 31 October.
“We will be consistent with obeying the law but also sticking to our policy, and you will have to wait and see what happens because there is a lot of days between now and 19 October,” he told the BBC’s Andrew Marr programme.
‘I don’t trust him an inch’
Shadow chancellor John McDonnell said the country was in “an extremely serious constitutional position” and that “no-one can trust” what might happen with Mr Johnson as PM.
“We’ve got to prevent Boris Johnson from forcing through a no-deal because of the damage it could do for our country,” he told Andrew Marr.
Mr McDonnell said he believed the prime minister might wait until no-deal was the only option, and an election would not solve the problem.
He said: “I think we’re in an extremely serious constitutional position.
“We don’t believe that we can pin him down and I don’t trust him an inch. I don’t think anyone does.
‘Irresponsible and elitist’
Shadow attorney general and Labour peer Baroness Chakrabarti called the government’s position “extraordinary and irresponsible”.
“I think the position is irresponsible and elitist – the idea there’s one law for Boris Johnson and his mates and another law for everyone else, it’s appalling,” she told Sky News’ Sophy Ridge on Sunday programme.
She added: “Every tin pot dictator on the planet throughout history has used the excuse of having the people on their side to break the law, to shut down Parliament, and all the rest of it.
“It’s absolutely extraordinary and I think it’s very un-British…”
She added that the legislation is “crystal clear” and Boris Johnson was “personally” duty-bound to comply with it.
‘Government must obey the law’
Amber Rudd, who quit the cabinet and surrendered the Conservative whip on Saturday, said the government “must obey the law”.
The former work and pensions secretary told Andrew Marr: “This government and any government must obey the law.
“I would urge Boris Johnson and his advisers to think very carefully about that.
In her resignation letter to Mr Johnson, she said she no longer believed leaving the EU with a deal is the government’s “main objective”.
What is the new law?
The bill, which is set to receive royal assent on Monday, was presented by the Labour MP Hilary Benn and backed by opposition parties and the recently expelled Tory MPs.
It gives Mr Johnson until 19 October to either pass a deal in Parliament or get MPs to approve a no-deal Brexit.
After this deadline, he would have to write to the EU asking for an extension to the UK’s departure date from 31 October to 31 January 2020.
The bill outlines the wording of the letter that the prime minister would have to write to the president of the European Council..
If the EU proposes a different date, the PM must accept it within two days.
But during this two-day period, MPs – not the government – would be able to reject the EU’s date.
Ministers will also be compelled to give the House of Commons Brexit progress updates over the following months.