NICOLA Sturgeon’s plan for Scotland to remain in the EU single market while the rest of the UK leaves in a hard Brexit is “highly unlikely” to succeed, one of her own advisers has said.

Dr Fabian Zuleeg of the European Policy Centre, and a member of the First Minister’s Standing Council on Europe since its creation in July, made the prediction to MSPs yesterday.

Ms Sturgeon will publish proposals to maintain Scotland’s relationship with the single market in the next few weeks, including plans for Holyrood having more powers over immigration and international relations.

Read more: Hard Brexit 'could cost Scotland £5bn in exports'

If Westminster rejects them, and Scotland is set to leave the single market, the First Minister has indicated she will call a second independence referendum before Brexit in 2019.

However giving evidence to the Scottish Parliament’s economy committee on the impact of leaving the EU, Dr Zuleeg poured cold water on the idea of a bespoke deal for Scotland.

He said there had been “quite a bit of speculation” that the financial sector could secure a special arrangement to passporting - the right to sell services freely across the EU - and that parts of the UK such as Scotland could likewise carry on in the single market.

He said: "There are some considerations as to whether there can be special deals.

“The one I think which is highly unlikely is a special deal for any part of the UK to remain in the single market.

"I wouldn't necessarily assume there will be a special deal for financial services in London.

Read more: Hard Brexit 'could cost Scotland £5bn in exports'

"I think there is relatively little incentive to give competitors good access to the market without any kind of give from the UK."

He said that as markets started to anticipate “a harder and harder Brexit, the bigger the costs are going to be,” as the UK would have to pursue its own trade deals with other nations.

"The question of assuming that there might be free trade agreements with all these places around the world, that might be the case but that's quite a big ask to negotiate," he said.

"It takes a lot time and will require quite a lot of giving up on the UK's side to actually get free trade deals with these places."

Also giving evidence, Dr Matias Margulis, an economist from the University of Stirling, said Brexit was a “Herculean task” for the UK government and could take decades to bed in.

It would also mean inferior trade deals compared to those the UK enjoyed as part of the EU.

He said it would require the UK to “not only renegotiate its trade relationship with the EU, but also with all the existing 50 countries the EU has... preferential trading agreements with that the UK currently enjoys. What we are looking at, at a safe estimate, is several decades of just renegotiating the current access the UK currently enjoys.

"The reality is the UK has not negotiated a trade agreement since the late 70s, it has no capacity to negotiate these agreements.

Read more: Hard Brexit 'could cost Scotland £5bn in exports'

“Nobody is getting in line to sign trade deal with the UK - it is not that important an economy globally. It is not the country most other nations are lining up to trade with. There has to be some realism of where the UK sits in the global picture."

A Scottish LibDem spokesman said: “Nicola Sturgeon won't want to hear this advice from one of her own advisers. She should put aside her obsession of independence and join our efforts to keep the whole of the UK in the EU."

A new study out today suggests Scotland's exports of goods and services could fall by £3bn and £2.3bn respectively in a hard Brexit.

A spokesman for the Scottish Government said it would set out proposals, including continuing membership of the single market, to protect Scottish interests by the end of the year.

“We will bring forward a detailed package outlining that in the next few weeks.”