NICOLA Sturgeon is to demand a radical package of powers be devolved from Westminster to Holyrood which would allow Scotland to remain in the European Single Market if the rest of the UK pursued a hard Brexit.

On Tuesday, Sturgeon will call for Scotland to be given power over immigration, business regulation, and employment rights.

The unveiling of the First Minister's battle plans over Europe, brings to an end the six months of phoney war between Westminster and Holyrood that has existed since the Brexit vote, and represents a hardening of the SNP's position in seeking to prevent Scotland being dragged out of the Single Market against the nation's will.

In a stark warning to Theresa May, Sturgeon also said that failure to agree to the proposals would mean a second independence referendum.

Sturgeon will publish a detailed paper on Tuesday proposing how Britain can remain in the single market allowing for free movement of goods, services and people - even though the UK has voted for Brexit.

Sturgeon's plan will also set out how Scotland can remain in the single market without the rest of the UK.

Writing in the Sunday Herald, ahead of the launch, Sturgeon said: "This is an important moment for Scotland – as the disastrous economic consequences of Brexit become ever clearer, it is vital that we find a way to protect Scotland’s interests."

Sturgeon's proposals will include the devolution of regulatory powers over goods, trade and business, which the SNP believes would allow Scotland to stay in the single market.

There will also be demands for the devolution of immigration powers aimed at allowing EU nationals living in Scotland to remain, as well as keeping employment rights that emanate from Brussels, but could be at risk after Brexit. More powers over taxation are also thought to be part of the plan.

The First Minister said the plan - which will fall short of Scottish independence - will form the basis of the SNP government's negotiations with Westminster over Brexit in the New Year.

However, Sturgeon warned that a total rejection of the plans by the Prime Minister would mean a second independence referendum.

Sturgeon said: "While we have of course not been involved in formal negotiations with other EU countries – that can only be done by the UK Government as the Member State – we have been busy ensuring that our position is understood by our friends and neighbours across Europe.

"But if our interests cannot be protected in this process, or are indeed brushed aside by the UK Government, then the people of Scotland should have the option of considering independence. That is why we are consulting on legislation that would allow another independence referendum to take place if necessary."

The Scottish Government's consultation on a 'draft referendum bill' is due to close next month. Sturgeon said her plan was based on "compromise and consensus", as she challenged the UK Government to accept it.

Details of the Brexit plans follow Sturgeon's establishment of an expert group - the Standing Council on Europe - to advise the best ways of maintaining Scotland's links with Europe.

The SNP leader said Scotland being dragged out of the Single Market would lead to tens of thousands of job losses and severely depress wage levels.

Sturgeon said: "When I unveil these proposals on Tuesday, I will be very up front. The best scenario for Scotland’s future in my opinion would be as an independent nation and a full member of the EU.

"But after the referendum, I said that in the spirit of compromise and consensus, I would examine all options - not just independence - and these proposals fulfil that commitment."

Sturgeon's Brexit minister, Michael Russell said the proposals would be put forward at the Joint Ministerial Committee meeting which will be held with the UK Government in the weeks and months ahead.

Russell said: "There is an overriding obligation on UK ministers to engage seriously with our proposals. The Prime Minister is on record as promising she would do so - and indeed that Scotland would be 'fully engaged' in the process - with Article 50 not being invoked until there was an agreed UK-wide approach."

However, the UK Government's Secretary of State for Scotland David Mundell said any plans from SNP ministers on Brexit must be "credible".

Mundell, the only Tory MP in Scotland, said: "We'll consider the Scottish Government's proposals carefully. I hope to see plans that are credible and backed up by evidence.

"I also hope they commit to working closely with us - in a Team UK approach - to get the best possible deal. That is how we will get the right deal for the whole of the UK - and the right deal for the UK will be the right deal for Scotland."