Embattled Theresa May has been branded a “pathetic coward” by Nicola Sturgeon after the Prime Minister pulled the crunch Brexit vote due tomorrow following private discussions with Cabinet colleagues.

READ MORE: Nicola Sturgeon: Delaying Brexit vote shows "pathetic cowardice" from Theresa May 

Mrs May is said to be preparing to travel to Brussels to win a "legally-binding assurance" that there will be a time-limit on the Irish backstop.

In dramatic developments, it was also announced that the PM will make a Commons statement at 3.30pm on “Exiting the European Union”.

The decision to pull the vote came after the PM held a conference call with senior colleagues to discuss the way forward as the parliamentary arithmetic continued to point to her suffering a humiliating defeat in tomorrow’s crunch vote on her Brexit Plan.

Suggestions that the vote has been pulled came just minutes after No 10 insisted it was going ahead.

While there was no official announcement from Downing Street, a senior source confirmed: "It's being pulled."

The First Minister swiftly took to Twitter: “If rumours of a delay are correct, it will be pathetic cowardice by a PM and government that have run out of road and now need to get out of the way.”

She later said: “It is final proof that the interests of a deeply-divided Tory Party matter far more to the Prime Minister than people’s jobs and living standards. That is an unforgiveable dereliction of responsibility and the UK Government should now get out of the way and allow others to take charge.

“It appears the vote is being delayed because of the Tory Party civil war and in a desperate attempt to save the Prime Minister’s job. Scotland voted overwhelmingly to remain but yet again our views are being ignored as they have been throughout this disastrous and incompetent Brexit process.”

Ms Sturgeon added: “The Prime Minister’s deal should come before the House of Commons immediately so that it can be voted down and we can replace Tory chaos with a solution that will protect jobs, living standards and Scotland’s place in Europe.” 

Jeremy Corbyn said the Conservative Government had decided the May Plan was “so disastrous” that it had taken the desperate step of delaying its own vote at the eleventh hour.

"We have known for at least two weeks that Theresa May’s worst of all worlds deal was going to be rejected by Parliament because it is damaging for Britain. Instead, she ploughed ahead when she should have gone back to Brussels to renegotiate or called an election so the public could elect a new government that could do so.

“We don't have a functioning government. While Theresa May continues to botch Brexit, our public services are at breaking point and our communities suffer from dire under-investment.

“Labour’s alternative plan for a jobs-first deal must take centre stage in any future talks with Brussels,” added the Labour leader.

His colleague David Lammy, speaking on behalf of the pro-EU Best for Britain campaign, said the decision to postpone the vote was an “unprecedented and historic humiliation” for the PM.

“After two years of negotiations with the EU, she is not even prepared to let MPs vote on her deal,” declared the Tottenham MP.

READ MORE: "We don't have a functioning government" Jeremy Corbyn hits out as Theresa May pulls Brexit vote 

"This is recognition of what has been clear for months: there is no majority for her miserable Brexit deal in Parliament,” added the Labour backbencher.

In the wake of reports that the Brexit vote had been called off, sterling fell 0.4 per cent against the US dollar to 1.26. Against the euro, the pound was down 0.6 per cent at 1.10.

Andrea Leadsom, the Commons Leader, said that there would be two more ministerial statements in the Commons.

She will give one on parliamentary business. It is thought that as tomorrow’s vote has been postponed, then so too will be the continuing debate on the Brexit Plan for today and tomorrow. Today’s was supposed to be on the Union.

Stephen Barclay, the Brexit Secretary, will also make a statement on Article 50. It is thought this will be in response to the ruling of the European Court of Justice, confirming that the UK could unilaterally stop Brexit.

However, the fact that Mrs May has decided to pull the vote following the insistence of senior colleagues throws up the possibility that she might go to Brussels in the next 24 hours to seek an extension to Article 50. This would give the UK and EU another couple of months to try to sort out a form of words on the Northern Irish backstop that could placate enough Tory MPs and possibly even the Democratic Unionists to back the Government motion on a meaningful vote some time in the New Year.

The developments in Downing St came as John Lamont, the Scottish Conservative backbencher, announced he would oppose the PM’s Brexit Plan.

READ MORE: Nicola Sturgeon calls on Labour to lodge vote of no confidence in Theresa May's government 

He tweeted: “I’m not a natural rebel. But I cannot support the Withdrawal Agreement. I have huge admiration for our Prime Minister. She’s been given an almost impossible task. But this Agreement threatens the integrity of the United Kingdom.”

Meanwhile, Kirstene Hair, the Tory MP for Angus, has come out in favour of the PM’s Brexit Plan, saying, while it was not perfect, “on balance, the responsible approach is to support this deal”.

Ross Thomson, the MP for Aberdeen South, opposes Mrs May's Brexit Plan, while Douglas Ross, the Moray MP, last month said he would find it "very difficult" to back it.

All the other eight Scottish Conservatives have come out in favour of the PM’s Brexit Plan.

However, discord has broken out within Tory ranks in Scotland with party sources suggesting some MPs have been either equivocal about their support for the May deal or have come out to oppose it because of their disappointment at not getting a government job.

One senior party source said some colleagues had a "beef" with David Mundell, the Scottish Secretary, over the fishing industry issue and were unhappy they had been passed over for junior Government roles.

“Claims they are undecided are completely disingenuous,” declared one insider. “People feel they have been overlooked. They are preparing to rebel for their own interests and not in the national interest.”

Another asked: “Are undecided Scottish Conservative MPs simply being ambitious? Apparently, they have so blotted their copy books only a change of leader gives them any hope. A new leader would mean a vacancy at Dover House[the Scotland Office].”

Elsewhere, figures showed that the UK Government spent almost £100,000 on Facebook adverts promoting Mrs May's Brexit deal in the lead-up to the Commons vote being pulled.

Facebook’s Ad Library Report showed that between Sunday December 2 and Saturday December 8 the UK Government spent £96,684 on 11 promotions on Facebook and Instagram, which is also owned by Mark Zuckerberg's firm.

They included videos on "What the Brexit Deal means for you - explained in 60 seconds", plus others focusing on immigration and jobs.

Others set out the benefits of the deal for Scotland, Wales and Northern Ireland specifically.