• May must change deal for another Brexit vote: Speaker
• May to seek Brexit delay of 3 months to two years: BBC

UK Prime Minister Theresa May's government has been plunged into constitutional chaos after the Speaker blocked the prime minister from asking MPs to vote on her Brexit deal for a third time unless it had fundamentally changed.

May held crisis talks with her ministers yesterday after the Speaker threatened to derail her EU withdrawal plan just 10 days before Brexit day, leaving her strategy in tatters.

May is still hoping she can get the divorce agreement she struck with the European Union through parliament before March 29, despite MPs having rejected it twice.

But in a dramatic ruling that prompted fury in government and warnings of a constitutional crisis, House of Commons speaker John Bercow said on Monday night he could not put it to another vote in its current form.

Weeks of chaotic political deadlock in parliament have already forced May to concede that Brexit must be delayed.

But she had been hoping to ask EU leaders for only a short delay when they meet at a Brussels summit on Thursday, warning that without a deal, any extension would be lengthy.

The BBC's political editor, Laura Kuenssberg, said May would ask for an extension until June 30 - which could give her another chance to get parliament to bless her deal - with the option of a delay of up to two years.

Pro-Brexit newspapers in Britain condemned Bercow as the "Brexit Destroyer".

Meanwhile, German Chancellor Angela Merkel said yesterday she would struggle until the last possible moment to achieve an orderly Brexit, saying the interests of Germany, Britain and the EU were at stake.

The Speaker's ruling adds further complexity to an already chaotic Brexit process that has exposed deep rifts in parliament. Several suggested that Bercow's ruling means May must now return to the negotiating table, even at this late stage. Constitutional experts suggested that if the EU agrees to an extension, that might also constitute enough of a change to have a vote after the summit, next week.

If a majority of MPs swing behind May's deal, they could pass a motion to force Bercow to allow another vote.