British Prime Minister Theresa May's bid to get her EU divorce deal through parliament was hit Monday with a bombshell announcement by the speaker, ruling MPs could not vote again on the same proposal they had already rejected.
With less than two weeks to go until a potentially chaotic departure on March 29 that could trigger an economic shock, May hoped to twist arms and have another vote on the withdrawal agreement by Wednesday.
Her government was scrambling to convince Brexit-supporting MPs to drop their opposition and support the twice-rejected deal.
But the speaker of parliament's lower House of Commons, John Bercow, issued an unexpected ruling that MPs could not be asked to vote again on the same deal in this session of parliament.
"What the government cannot legitimately do is resubmit to the house the same proposition, or substantially the same proposition," he said, citing precedent dating back to 1604.
It is the first time in more than a century that a parliamentary speaker has invoked the rule.
Responding to MPs' questions about his ruling, Bercow said that "in all likelihood" it meant the government must find a way of substantially altering the deal with the EU before it can be voted on again.
A government source told AFP the speaker's move suggested "what he really wants is a longer extension, where parliament will take over the process and force a softer form of Brexit."
May had hoped to win last-ditch approval for her plan by Wednesday, before heading to an EU summit in Brussels on Thursday and Friday and seeking a short technical delay to Brexit until June 30.
If MPs have not rallied round a deal by the summit, she has vowed to request a longer delay.
Solicitor-General Robert Buckland, a Conservative MP who gives legal advice to the government, told the BBC Bercow had plunged Britain into "a major constitutional crisis".
He suggested parliament could have to be broken up early before reconvening in a new session, to bring the same deal before MPs.
European foreign ministers meeting in Brussels for pre-summit talks on Monday were broadly supportive of granting a delay but questioned its purpose.
"We are not against an extension in Belgium but the problem is to do what?" Belgian Foreign Minister Didier Reynders told reporters.
Brussels could handle a British request to delay Brexit received at any time right up to the final hour before the 11:00pm London time March 29 deadline, a senior EU official told reporters.
British junior Brexit minister Kwasi Kwarteng told MPs the government expected European leaders to decide on the extension request at the summit, with legislation to change the UK's exit date then following next week.
May's allies had argued earlier Monday that the government was convincing ardent Brexiteers previously opposed to her plan.
Foreign Secretary Jeremy Hunt said there were "cautious signs of encouragement" but admitted there was a "huge amount of work to do" to win over hardcore Brexiteers.
Jacob Rees-Mogg, leader of the Conservatives' ardently pro-Brexit European Research Group (ERG), hinted on LBC radio that he could soften his position if Northern Ireland's small Democratic Unionist Party (DUP) agreed.
"No deal is better than a bad deal but a bad deal is better than remaining in the European Union," he said.
The DUP -- which May's Conservatives rely upon for a slender majority in parliament -- has so far rejected the deal and is seen as crucial in determining its ultimate fate.
"Talks have been taking place with the DUP. Those talks are continuing," the prime minister's spokesman said.
However, in a blow to May, 23 Leave-backing Conservatives wrote a joint letter to The Daily Telegraph calling for a no-deal exit.
Former British foreign secretary Boris Johnson, a pro-Brexit figurehead, urged her to use the EU summit to wring more concessions out of the bloc before risking a third vote.
He summarised the dilemma as being between a deal that is "detrimental to the interests of this country" and the "real risk that Brexit would not happen at all".
"It is not too late to get real change," he wrote in the Telegraph.