Theresa May has called off and deferred Tuesday's crucial vote on her Brexit deal in the face of what was likely to be a significant defeat by Conservative party rebels.

The prime minister told MPs about the delay in a statement in Parliament on Monday afternoon.

The pound fell sharply in response, shedding 0.5 percent versus the US dollar to stand at $1.26, an 18-month low after May's remarks.

The prime minister said she believed she could still get the deal through if she addressed MPs' concerns. May said MPs backed much of the deal she has struck with the EU but there was concern over the Northern Irish backstop.

May again rejected all other alternatives that have been proposed to her deal - including a further referendum and leaving without a deal.

She told MPs she would be speaking to EU leaders ahead of a summit later this week, about the "clear concerns" expressed by MPs.

Labour leader Jeremy Corbyn said the prime minister had "lost control of events" and the government was in "complete chaos" - and urged her to stand down.

Meanwhile, European Unions' top court ruled that the UK can revoke Brexit without permission from the 27 other EU member states.

A judgement by the European Court of Justice (known as the ECJ) gives the UK the right to unilaterally withdraw its Article 50 notificationto leave the EU.

In a statement, the ECJ said: "In today's judgment, the full court has ruled that, when a member state has notified the European Council of its intention to withdraw from the European Union, as the UK has done, that member state is free to revoke unilaterally that notification."

Campaigners had argued that the option of remaining in the EU be clear to parliamentarians making decisions on Britain's future in regards to the EU.

Theresa May has strongly denied that remaining in the EU is an option.

On Sunday, one of May's closest Cabinet allies issued a blunt warning that the UK should learn from Northern Ireland about "the damage that division can do".

The Northern Ireland secretary, Karen Bradley, writing for the Guardian newspaper on Sunday, warned that divisions caused by Brexit could scar the whole of the UK in a similar way to the historic divides that have split Northern Ireland.

"When the dust settles on Brexit, we must move forward in order to put some of the division about the nature of our country's relationship with the European Union behind us. Northern Ireland, in particular, knows the damage that division can do, and the benefits when that division can be overcome."

Amid deep anxiety and uncertainty over the fate of her deal, the prime minister spoke by phone to Donald Tusk, the European council president, to discuss the bleak prospects for it being voted through in Parliament. Tusk later tweeted it was "an important week for the fate of Brexit".