Esther McVey has quit her post as Work and Pensions Minister over the Brexit divorce deal.
The Tatton MP resigned from her post on Thursday morning saying "it was obvious to everyone" the EU withdrawal deal "did not honour the result of the referendum."
In her fiery resignation letter, she said Theresa May's plan "threatened the integrity of the United Kingdom" and that she "could not look her constituents in the eye" were she to vote for it.
She said: "This is a matter of trust. It is about the future of our country and the integrity of our democracy.
"The deal you put before the Cabinet yesterday does not honour the result of the referendum. Indeed, it doesn't meet the tests you set out from the outset of your premiership."
She added: "British people have always been ahead of politicians on this issue, and it will be no good trying to pretend to them that this deal honours the result of the referendum when it is obvious to everyone it doesn't.
"We have gone from no deal is better than a bad deal, to any deal is better than no deal.
"I cannot defend this, I cannot vote for this deal. I could not look my constituents in the eye were I to do that. I therefore have no alternative but to resign from the Government."
She added that the proposals put before Cabinet, in a mammoth five-hour meeting on Wednesday night, meant handing over £39bn to the EU "without anything in return".
"It will trap us in a customs union, despite you specifically promising the British people we would not be," she said.
Ms McVey went on: "We wouldn't be taking back control, we would be handing over control to the EU and even to a third country for arbitration."
Ms McVey has been Secretary of State for Work and Pensions since January this year.
She was elected MP for Tatton in 2017 having lost her Wirral West seat, which she held for five years, in 2015.
Ms McVey had always openly refused to back the Prime Minister's Brexit Chequers plan.
