"Where some of its most senior people who hold the greatest offices of state, at every twist and turn, when our Prime Minister moves towards securing a Brexit that will serve everybody in our country, the softest, most sensible Brexit, both publicly and privately they undermine her and scupper her attempts".
His resignation didn't prompt an immediate response from the government, but at the eleventh hour, ministers evidently feared a Commons defeat.
But Tuesday's victory came at a cost - a government promise to strengthen Parliament's voice, potentially at the expense of its own power to set the terms of any final divorce deal with the EU. The upper chamber, the House of Lords, inserted amendments in 15 areas to soften the departure.
Addressing Conservative backbenchers in Westminster on Monday evening, the Prime Minister warned if a series of Lords amendments to the EU Withdrawal Bill are approved by MPs, it will send the wrong message to Brussels. That clause - drafted by Grieve - basically hands a lot of power to Parliament if no deal has been agreed by the end of November. If the government fails to pass the bill as it is, it will be forced to change what it asks for in negotiations with the European Union -undermining May's position and possibly threatening her job as Prime Minister.
They are most anxious about a vote on Wednesday requiring the government to make a statement on its efforts to negotiate a customs union with the EU.
The result followed a day of high drama as a justice minister in May's government resigned in order to back the amendment. A victory for the "meaningful final vote" amendment would leave the government weaker in am upcoming round of talks with European Union negotiators in late June, and also weaken Theresa May's authority as leader.
The opposition leader said: "We can not settle for this".
Tory chief whip, Julian Smith, scurried up and down the green benches of the Commons, speaking urgently to groups of MPs including Grieve.
Brexit campaigners still expressed concern that the concession may open the door to the European Union trying to force Britain into retaining the closest possible ties with the bloc by weakening the government's hand in the talks.
"A vote between bad and worse is not a meaningful vote".
Dismissing the Government's compromise, she tweeted: "Merely issuing a statement in response would make it a meaningless final vote".
May urged Conservative lawmakers to back the government and show "that we are united as a party in our determination to deliver on the decision made by the British people".
The major last-minute concession by ministers means the government avoids defeat by 324 to 298.