The SNP is committed to a reunion with Brussels if they succeed in breaking away from the United Kingdom, with Ms Sturgeon on record believing such an outcome could be delivered "relatively quickly". However, Kevin Hague, chairman of the pro-Union think tank These Islands, and a regular critic of the feasibility of the SNP's independence plans, said the situation was not so simple as Ms Sturgeon made out.
He pointed to the Acquis communautaire, a sprawling amalgamation of rules, regulations, court decisions and other documents which constitutes the body of European Union law - and specifically chapter 17, which sets out the fiscal requirements for countries seeking to join the EU.
Among other rules, the Acquis requires the independence of central banks in Member States, prohibits direct financing of the public sector by central banks, and requires member states to co-ordinate their economic policies and be subject to the Stability and Growth Pact on fiscal surveillance.
Crucially, before adopting the euro as their currency, the regulations required new members to have one of their own, Mr Hague pointed out.
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Nicola Sturgeon talks to Andrew Neil last year
He told Express.co.uk: "Scotland would need to have established its own central bank and currency."
Additionally, the Scottish government would need to be able to demonstrate it was on course to run a budget deficit of less than 0.5 percent of GDP, Mr Hague explained.
Referring to figures carried in the Government Expenditure and Revenue in Scotland (GERS) plan 2018/19, Mr Hague added: "So establishing a currency and not just getting below the excessive deficit threshold (three percent of GDP) but being on a path to comply with the fiscal compact (0.5 percent of GDP) means some combination of massive tax rises and/or public spending cuts, given the latest Scottish deficit was seven percent of GDP."
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Nicola Sturgeon pictured at Holyrood
Tax rises risked capital flight, while spending cuts may also damage the revenue side if they caused economic slow-down, Mr Hague warned.
To illustrate the scale of the challenge to get from 7 percent of GDP to 0.5 percent of GDP though public spending cuts alone he added this would require public spending to be cut across the board by 16 percent (£11.7bn).
Mr Hague said: "It’s no co-incidence that this is similar but bigger than the £10.7bn fiscal transfer, because the UK’s deficit is 1.1 percent of GDP.
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"To put that £11.7bn in context, the total Scottish education spend is £8.5bn, health spend is £13.1bn.
"It's fair to say the SNP is in for a nasty shock if they think they can join the EU seamlessly and without significant economic hardship.
"I’d suggest that the welfare state as we know it would not survive the break-up of the UK.
"To quote English historian Peter Hennessy, the creation of the welfare state delivered 'equality of benefit for all as a bonding of a common citizenship'.
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"That bonding of a common citizenship would be lost."
Speaking to the BBC's Andrew Neil last year, Ms Sturgeon refused to offer a specific timescale for an independent Scotland rejoining the EU.
However, she added: "In all of my experience of discussions with different interests in the European Union I think that could be relatively quick but that will depend on the discussions we have.
“We understand the conditions we would require to meet and the discussions that would require to take place but if we’re in a position of Scotland being taken out of the European Union then we will be seeking a way back in.”"
A sticker on the border between England and Scotland
Addressing the currency issue, she added: "We would be setting up a central bank, we would be setting up the infrastructure that is required for that, that is part of the discussion we would have about the European Union, but it is not true to say we would have had to have established an independent currency before joining the European Union.
"We would have a discussion with the EU about the journey an independent Scotland was on in terms of currency, and the accession if Scotland was already out of the EU to the point where we rejoined the EU."
Express.co.uk has contacted the SNP to ask for an explanation of the SNP's official policy with regard to an independent Scotland joining the European Union, as well as whether the party was confident it would be able to comply with the fiscal requirements set out in the Acquis.