The SNP has urged Theresa May to take the three million EU nationals living and working in the UK, including 186,000 in Scotland, “out of limbo” and guarantee them their citizenship rights.

Stephen Gethins, the party’s Europe spokesman, warned the Prime Minister in a letter that the Conservative Government’s failure to provide such a guarantee was acting as a “deterrent to the top talent” the country needed to attract.

Read more: Brexit is firing gun to "decade of disruption" for the UK, warns landmark IPPR report

“As we move towards 2017 the UK Government must finally end its disgraceful treatment of EU nationals and give them the reassurance that they will be able to continue living and working in Scotland and elsewhere in the UK,” declared the Fife MP.

“It is unacceptable that families who have done us the honour of making Scotland their home have been left in limbo for more than six months now. The uncertainty and damaging rhetoric we have seen from the UK Government is driving away the top talent we need and it is forcing families to reconsider their future here.”

Mr Gethins argued that it was highly detrimental to the UK economy and deeply unfair to families for the Conservative Government “to continue to leave EU nationals in limbo” over their residency status and rights.

“EU nationals make a huge and valued contribution to our society; they are our friends, neighbours and colleagues, they benefit our economy, they play a vital role in our public services and they make our society richer and more diverse.

“There is wide consensus that EU nationals living and working here should be guaranteed their residency rights; it is time for Theresa May to listen and act,” added Mr Gethins.

Read more: Brexit is firing gun to "decade of disruption" for the UK, warns landmark IPPR report

The PM has made clear she wants an early resolution in the Brexit talks to the issue of citizenship rights for EU nationals living in the UK but has also insisted there has to be reciprocity, whereby those Britons living on the continent also have their rights protected too.

Meantime, Mrs May was accused of making up her Brexit strategy “on the back of a fag packet” by Tim Farron, the Liberal Democrat leader, after the head of the senior civil servants union, the FDA, warned her of the under-resourcing of Whitehall departments to cope with the complexities of the Brexit process.

Dave Penman said: “Ministers lack the political courage to admit how complex and time-consuming this will be. When anyone pops their head above the parapet – former Permanent Secretaries, ex-Cabinet Secretaries, the Institute for Government – and says this is going to take a long time and it’s complex, they are immediately shot down and accused of betraying the will of the people.

“The politics around Brexit are the biggest risk to Brexit. The Government is clearly in a situation where they are trying to deny the complexity of it,” insisted the Scot.

Read more: Brexit is firing gun to "decade of disruption" for the UK, warns landmark IPPR report

Elsewhere, Migration Watch UK claimed immigration from the EU would remain high if Britain stayed in the European single market after Brexit.

The group, which campaigns for tighter immigration controls, estimated that net migration from the bloc would be unlikely to fall below 155,000 a year in the medium term in those circumstances.

In response, Mr Farron said: “It's no surprise Ukip's favourite think-tank is pushing for a hard Brexit that would rip Britain out of the single market, costing jobs and risking the livelihoods of thousands of British people."

Noting how a recent opinion poll showed that nine out of 10 people wanted Britain to remain in the single market, the Cumbria MP added: “The Liberal Democrats are proud to be the party of common sense, providing the real opposition to the Conservative Brexit government by fighting to remain in the world’s most lucrative market.”