Amber Rudd has quit the cabinet and surrendered the Conservative whip, saying not enough effort is going into getting a Brexit deal.
The former work and pensions secretary told the BBC there were no “formal negotiations” taking place with the EU, just “conversations”.
Ms Rudd said up to 90 per cent of government time was spent preparing for an “inferior” no-deal option.
Chancellor Sajid Javid said he was “saddened” by the resignation.
He told the BBC’s Andrew Marr Show the government had been putting a “tremendous amount of effort” into getting a new deal with the EU.
He added that preparations for a no-deal scenario would “concentrate minds” in Europe regarding working towards a new agreement.
Downing Street has announced that Environment Minister Therese Coffey will replace Ms Rudd as work and pensions secretary. In her resignation letter to PM Boris Johnson, Ms Rudd said: “I joined your cabinet in good faith: accepting that ‘No Deal’ had to be on the table, because it was the means by which we would have the best chance of achieving a new deal to leave on 31 October.
“However I no longer believe leaving with a deal is the government’s main objective.”
She also criticised the PM’s decision to expel 21 MPs from the parliamentary Conservative party after they rebelled against him last week over a bill designed to avoid a no-deal Brexit, calling it an “act of political vandalism”.
Having given up the Tory whip, the MP for Hastings and Rye, who supported Remain in the 2016 referendum, will remain an MP but will no longer sit as part of the Conservative party in Parliament.
“I will be considering my position – whether I will stand as an independent Conservative should there be an election coming up,” she told the Sunday Times.
What has the reaction been to her resignation?
Health Secretary Matt Hancock said the Conservative Party had “always been a broad church” and he was “gutted” to see Ms Rudd leave.
Former Foreign Secretary Jeremy Hunt said Ms Rudd’s departure was “desperately sad news”, describing her as “one of the most principled and capable ministers I’ve worked with”.
Shadow Brexit secretary Sir Keir Starmer tweeted that her departure showed Mr Johnson’s government was “falling apart”.
Labour Party chair Ian Lavery said the resignation was a sign that “no one trusts” Mr Johnson. “The prime minister has run out of authority in record time and his Brexit plan has been exposed as a sham,” he said.
SNP Westminster leader Ian Blackford called on the prime minister to resign, arguing he had “no support or credibility left”.
“Boris Johnson’s Tory government is on the verge of collapse – with no majority, no mandate and no right to pursue its reckless plans to impose an extreme Brexit,” he said.
PM Boris Johnson is reportedly considering defying a new law aimed at forcing him to seek an extension to the Brexit deadline if MPs fail to approve either a new deal or a no-deal exit by 19 October.
A senior No 10 source told The Sunday Times: “If there isn’t a deal by the 18 [October] we will sabotage the extension.”
Mr Javid said the government would obey the law, but the prime minister will “absolutely will not ask” for a further delay at an EU summit in mid-October.
“The bill talks about 19 [October] being an important date, and at that point we will consider our options,” he told the BBC.
“We will obey all laws because all governments should obey laws absolutely, but you will have to wait and see what happens then.”
According to the Sunday Telegraph, Downing Street says Mr Johnson “does not share the rebel interpretation” of the new law – expected to gain royal assent next week. The bill was drawn up by cross-party MPs, including 21 Tory rebels who have since been ousted from the parliamentary party.
It is thought that Mr Johnson believes he could legally disregard some or all of the bill’s requirements – a move that could see him hauled before the courts and potentially facing prison.
This, in turn, could trigger an emergency judicial review by the Supreme Court next month, leading to a court showdown over whether the UK would be able to leave the EU with no deal on 31 October.
On Sunday, Foreign Secretary Dominic Raab told Sky News the government will “look very carefully” at its “interpretation” of the legislation.
Mr Johnson has written in the Mail on Sunday and Sunday Express that on Monday he will offer Labour leader Jeremy Corbyn “one last chance” to agree to an early election.
Opposition parties have agreed not to back his demand for a general election before the EU summit in mid-October, and say they will vote against the government’s proposal at a vote on Monday.
If Mr Corbyn refuses, Mr Johnson said “this government will simply carry on”.
Writing in the Sunday Telegraph, Brexit Secretary Steve Barclay said “we are doing everything we can” to reach a deal.
But he said the EU were setting a test on the Irish backstop arrangement that is “impossible to meet”.
The backstop – a position of last resort to maintain a seamless border on the island of Ireland – is proving a serious obstacle to Mr Johnson’s Brexit plans.
Mr Barclay said the government is proposing “reasonable alternative solutions” but he objected to the EU’s demand for “molecular detail” on how they would work before 31 October.
An Edinburgh University graduate, she previously worked in banking and recruitment
She was credited as a consultant on the 1994 hit film Four Weddings and a Funeral
In the 2016 Tory leadership debates, she described Boris Johnson as the “life and soul of the party but not the man you want driving you home at the end of the evening”.
