“As prime minister, I am not prepared to delay Brexit any further than 30 June,” she told MPs – later repeating the statement to drive home the message.
Ms May launched an extraordinary attack on MPs for twice voting down her Brexit agreement, accusing the Commons of “contemplating its navel”.
But Jeremy Corbyn blamed the prime minister for causing a national crisis, saying her “concerted campaign of blackmail, bullying and bribery” had failed to persuade MPs or the country to back her deal.
Ms May also raised the stakes by insisting a crash-out Brexit is still possible, even if delayed until June, warning MPs: “This does not take no-deal off the table.”
However, moments after finally sending her extension request letter to Brussels, she was forced to concede she could not say if or when MPs would approve her deal.
It stated a long delay would require UK participation in May’s European Parliament elections, which the prime minister insisted was unacceptable.
The prime minister will formally make her request to summit of EU leaders on Thursday, where the unanimous approval of all 27 remaining member states is required for any extension.
However, at PMQs 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, 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.
In an unprecedented attack on the power of MPs, Ms May said: “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.”
Later, Ms May’s repeatedly failed to give a clear answer over whether her words definitely meant she would resign rather than seek a long extension.
Asked if she would step down, her spokesman said: “She believes that what she has set out in the letter, and what she’s asking for in terms of that short extension to 30 June, is the best way of seeing the deal ratified.
“She believes that is manifestly in the interests of the people of this country and that is her focus.”
Asked again he said: “I think it’s important that the PM sends a very clear signal about her view of the right way forward and I think that is precisely what she’s done by saying…she doesn’t believe a long extension is the right thing to do, she doesn’t think more navel gazing will help solve the problem, so she’s sending a strongest signal about her opinion, which is we need to get this done, we need to deliver for people and that means not delaying it beyond the date.”
Pushed again, the spokesman said: “What you should infer is her determination to get this over the line.”