LONDON (Reuters) - Prime Minister Theresa May’s government and the European Union should begin planning for a second Brexit referendum because parliament cannot agree on a divorce deal and voters will be asked to break the deadlock, opposition lawmakers said.

Slideshow ( 6 images )

Less than four months until the United Kingdom is due to leave the European Union on March 29, Brexit was plunged into chaos on Monday when May accepted that British lawmakers would not accept her deal and withdrew a key vote on it.

The ultimate outcome of Brexit is now uncertain. Possible scenarios include May’s deal ultimately winning approval in a new parliamentary vote; May losing her job; Britain leaving the bloc with no deal or another referendum.

“The UK is in the middle of a constitutional crisis, which is unparalleled in modern history,” said Ian Blackford, the leader of the Scottish National Party in Westminster. “There now appears to be scant potential for consensus to be found.”

May has repeatedly said that British lawmakers face a choice of approving her deal or facing an exit with no deal or even the reversal of Brexit. So far there has been no indication that the government has been preparing for a second vote.

Liberal Democrat leader Vince Cable said the government must ask the Electoral Commission, the independent body which oversees referendums, to begin looking at what question might be asked and when another vote could be held.

A new vote, Cable said, must ask whether voters wanted a Brexit deal or to stay in the EU. He said a “no deal” exit should not be one of the options.

“You prepare for what might happen rather than what you want to happen,” he said.

His comments were echoed by Blackford, the Green Party, the Welsh nationalist party, the Labour Party’s Margaret Beckett and the Conservative lawmaker Anna Soubry.

Bookmakers are offering almost an even chance of another EU referendum before 2020.

An array of smaller parties including the SNP and the Liberal Democrats said European leaders should prepare by agreeing to allow an extension of Britain’s Article 50 departure notification.

Blackford also issued the opposition Labour leader Jeremy Corbyn with an ultimatum to call a vote of no-confidence in the government or they would attempt to do so without them.

“This is a government that is in chaos and crisis and that is why I would appeal to Jeremy - we have no option,” he said.

“We cannot delay and if Jeremy does not accept that responsibility then I am afraid the rest of us will have to accept that responsibility.”

On Monday the speaker of the House of Commons John Bercow said that while smaller parties could table a no-confidence motion, it was usually only put forward for a debate and vote if it came from the main opposition party.