The Prime Minister met leaders of the devolved administrations in the hope of building support for her Withdrawal Agreement.

Theresa May’s plans for securing reassurances from Brussels on her Brexit deal are “a wee bit nebulous”, Scottish First Minister Nicola Sturgeon has said.

Speaking after talks with Mrs May in Downing Street, Ms Sturgeon echoed the remark of European Commission president Jean-Claude Juncker which infuriated the Prime Minister at last week’s EU summit.

The comment came as Home Secretary Sajid Javid launched the Government’s plans for immigration policy after Brexit, which Ms Sturgeon said amounted to an “act of vandalism” on the Scottish economy.

Meanwhile, in Brussels, the European Commission activated plans for a possible no-deal Brexit on March 29, making clear that they are designed to “protect the vital interests of the EU”.

A day after the Cabinet gave the green light to full-scale no-deal preparations in the UK and 100 days before the scheduled date of Brexit, the Commission said it was “essential and urgent” to act to avoid “major disruption” if the UK crashes out without an agreement.

Plans cover 14 areas most likely to be affected, ranging from financial services to aviation, customs and carbon emissions trading.

Business groups issued a stark warning of the threat of no-deal Brexit, saying many firms are now reaching “the point of no return”.

In a joint statement, the UK’s five main business organisations said contingency plans for a no-deal were a “significant drain” on companies’ time and money.

Firms are pausing or diverting investment that should be boosting productivity, jobs and pay, said the British Chambers of Commerce, CBI, EEF, Institute of Directors and Federation of Small Businesses.

Mrs May is understood to have urged leaders from the devolved administrations to “pull together” to back the Withdrawal Agreement she reached with Brussels in November.

The Prime Minister met the First Ministers of Scotland and Wales and representatives of the Northern Ireland Civil Service at a gathering of the Joint Ministerial Committee in Downing Street as she seeks to build a Commons majority for her deal.

But as she emerged from Number 10, Ms Sturgeon restated the Scottish National Party’s determination to vote against the deal when it returns to the Commons in January.

Prime Minister Theresa May visited Heathrow Airport to publicise the Government’s immigration plans (Niklas Halle’n/PA)

And she said it was “unacceptable” for the PM to delay the vote in the hope of “running down the clock” to Brexit and leaving MPs with the choice only between her deal and no deal.

Ms Sturgeon, who backs a referendum on the final terms of the Brexit deal, said: “It’s beyond me that any Prime Minister would want to have as her legacy turning the UK inwards and making it less open and welcoming to people from the rest of the world.”

On a visit to Heathrow on Wednesday, Mrs May said that the UK was “talking to the EU about some further assurances to assuage the concerns that Members of Parliament had on a particular issue in the Withdrawal Agreement”.

But asked if the PM had spelt out what was being done, Ms Sturgeon said: “It was a wee bit nebulous. There’s not a lot of detail there.

“She says she’s working with the EU, trying to find assurances. I pressed her to give a bit more detail on that. I have to say it wasn’t forthcoming.”

Welsh First Minister Mark Drakeford told reporters in Downing Street that a second referendum would be “unavoidable” if no deal was agreed by MPs and there was not a general election.

“The Prime Minister should put her deal to the House of Commons and see what support she can mobilise for it and see whether there are any alternatives – a Norway-plus arrangement for example – that might have a better chance of responding to where the centre of gravity in the House of Commons may currently lie,” he said.

“If the House of Commons is deadlocked we need a general election and a new House of Commons.

“If we are denied that then it seems to me unavoidable that the decision would have to go back to the people.”

In the Commons, shadow Brexit secretary Sir Keir Starmer said Labour MPs would not be forced by the shortness of time into choosing between Mrs May’s deal and no deal.

In a debate called by the opposition, Sir Keir said: “I don’t think for one moment that this House if going to accept the binary choice that the Prime Minister will attempt to put before us.

“A choice between bad and even worse is not a meaningful choice. Nor is leaving the EU on March 29 next year without a deal viable.

“It has never been viable and as every day goes past it becomes less and less viable.”

Sir Keir said that “serious consideration” should be given to extending the two-year Article 50 process leading to Brexit on March 29 2019.

Environment Secretary Michael Gove acknowledged that a no-deal Brexit would have a “negative economic effect”.

But he told the Commons Environmental Audit Committee: “It is also the case that those impacts will be acute for a short period and mitigable – not totally but to an extent.”

And he reassured MPs: “Supplies of ambient products that are stored without chilling or freezing, I think will be fine. If people want Belgian beer or French wine, I don’t think that’s going to be an issue.”