NICOLA Sturgeon’s plan for a bespoke Brexit would have caused “significant disruption” to business, the Brexit Secretary told SNP ministers in a previously secret rejection letter.

David Davis told the Scottish Government last month that the First Minister’s plan to keep Scotland in the EU single market after Brexit would create "barriers" to trade within the UK

He also said he was “disappointed” Ms Sturgeon had called for a second independence referendum while the UK and Scottish governments were still discussing her plan.

In response, the SNP Brexit minister Michael Russell said that “with the necessary political will and commitment” the objections could have been overcome.

Ms Sturgeon published Scotland’s Place in Europe, her detailed plan to keep Scotland in the single market after the rest of the UK left, last December.

It suggested Scotland could be a Norway-style member of the single market through the European Economic Area (EAA) or European Free Trade Association (EFTA).

Free movement of goods, capital, services and labour with the EU would have continued, although Scotland would not have had a say in writing EU rules.

The SNP government admitted the plan was politically and technically challenging, and would need Holyrood to get new powers over immigration, workers’ rights and international deals.

It would also have relied on the UK making sacrifices in negotiations with the other 27 EU nations to secure a bespoke deal for Scotland.

After Ms Sturgeon called a second referendum in mid-March, the UK government rejected the plan, but refused to publish the letter it sent to the Scottish Government.

After a war or words between Edinburgh and London over who should release it, Mr Russell gave the correspondence to MSPs and put in on the government’s website.

In his March 29 letter, Mr Davis said the two governments shared a desire for “the freest and most frictionless trade with EU”, despite disagreement over the means.

But he said of Ms Sturgeon’s plan for staying in the single market: “As the Prime Minister has made clear, this is simply not possible if we wish to take back control of borders and immigration in the way people in Scotland and the rest of the United Kingdom desire, nor if we wish to enjoy the supremacy of our domestic courts.

“There are clear barriers to making your proposals a reality. Scotland’s accession to EFTA, and then the EEA, would not be deliverable and, importantly, would require the consent of all EFTA and EU member states.

“Any divergence between EU and UK law - as a result, perhaps, of new EU regulation - could lead to the creation of new barriers to trade within our Union, which could take the form of additional controls and checks on trade within the United Kingdom.

“Given that trade with the rest of the UK is worth four times trade with the EU, I do not believe that such significant disruption to the internal UK market is in Scotland’s - or the UK’s - best interests. And Scotland’s businesses could face a confusing mix of regulatory regimes.”

He added there had been "a good deal of resource" spent on studying the plans, and he was "disappointed that the Scottish Government has called for another referendum on independence before we were able to discuss the outcomes of this joint work, that was entered into in good faith.”

Replying on April 12, Mr Russell restated the “fundamental importance” his Government placed on single market membership.

Referring to the 69-59 vote by MSPs in favour of Holyrood getting referendum powers, he said: “The Scottish Parliament has now agreed an independence referendum should be held once there is clarity over the outcome of the Brexit negotiations so that the people of Scotland have an informed choice over their future.

“In relation to the specific points you raise regarding the proposals in Scotland’s Place in Europe, there is every reason to suggest that with the necessary political will and commitment these issues could have been addressed.

“Indeed there were no insurmountable issues raised in the engagement between officials.”

He rejected Mr Davis’s assertion that London and Edinburgh agreed on the “large majority” of subjects, and said ministers in the devolved administrations in Wales and Northern Ireland also felt “frustration” at the UK government’s approach.

Calling for further talks on Brexit, he said: “We must reiterate our view that these should be meaningful, based on trust, openness and a genuine sharing of options and policy positions as well as data, and must give real opportunities to influence the process."

Scottish LibDem leader Willie Rennie said: “The SNP claimed that their tissue thin proposals were compromises but they were about generating grievances.

“The only option the First Minister really wants to succeed is independence. The SNP are using EU supporters to push for a referendum but will sell them out to get independence.”