In a powerful speech, the former attorney-general condemned the prime minister for blaming the Commons for the crisis while refusing to accept any responsibility herself.
“I have never felt more ashamed to be a member of the Conservative Party or to be asked to lend her support,” Mr Grieve told MPs.
“She spent most of her time castigating the house for its misconduct. At no stage did she pause to consider whether it is, in fact, the way she is leading this government that might be contributing to the situation.”
The pro-EU Tory said he had long considered Ms May to be “a friend”, but added: “I have to say I could have wept – wept to see her reduced to these straits.
“And wept to see the extent to which she was now simply zig-zagging all over the place, instead of standing up for what the national interest must be.”
Unless the prime minister changed course “at the 11th hour and 59th minute”, the UK would “spiral down into oblivion, and the worst part of it all is that we will deserve it”, Mr Grieve added.
The fierce criticism came after Ms May used prime minister’s questions to lay into MPs for twice rejecting her deal – and for threatening to do so a third time.
Explaining why she was not seeking a long Brexit delay, she told the Commons: “The outcome of a long extension would be endless hours and days of this house carrying on contemplating its navel on Europe and failing to address the issues that matter to our constituents.
“This house has indulged itself on Europe for too long. It’s time for this house to determine that it will deliver on Brexit for the British people.
“That’s what the British people deserve. They deserve better than what this house has given them so far.”
The comments came during a stormy prime minister’s questions, during which MPs lined up to attack Ms May’s plan to ask the EU for only a short extension to the Article 50 process.
She was bombarded with criticism that a short delay – even if granted – would achieve nothing, given the logjam at Westminster.
It was pointed out that the decision flew in the face of the motion, passed by MPs last week, for a long delay if – as has happened – the government was still unable to pass its agreement.
The deal now looks even more doomed, because Brexiteer MPs are even less likely to abandon their opposition with the threat of a long extension evaporating.
Furthermore, speaker John Bercow has warned he will not even allow a third meaningful vote unless the proposal before MPs has “significantly changed”, which the EU has ruled out.
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