THE UK could be plunged into an “extraordinary” political and constitutional crisis in the event of a vote for Brexit even without a second independence referendum being held, it has been claimed.

Scotland could instead block and stall the process of the UK getting out of Europe by refusing to co-operate with necessary repealing or amending legislation, according to Kirsty Hughes, an associate fellow with Friends of Europe, a EU think-tank which states it is independent.

She argued it could even create an “explosive” scenario where Westminster may be faced with having to overrule the Scottish Parliament to push necessary legislation through.

Hughes, who has been a senior political adviser in the European Commission, said the idea of blocking or stalling Brexit was one option for Scotland if it faced being dragged outside the EU against its will.

She said: “It looks at the moment, unless something incredibly big and unpredictable happens, you would expect Scotland and Northern Ireland would vote to stay in and that Wales might vote to stay in.

“But I think unless all four vote to stay in, you have got a pretty big political problem – if it is the UK stays in but England voted out then you have got one sort of problem and a very profound one, but I think if it is the other way round, it is the most immediate and big crisis.”

Hughes, who has published a report on Scotland and Brexit and gave evidence to Holyrood’s European Affairs Committee on the issue of EU reform last week, said in this scenario, the devolved administrations could choose not to cooperate by repealing or amending legislation which was required to exit the EU.

She added: “It would be an extraordinary political and constitutional crisis, and I think in the short-run - even if the SNP was considering a referendum - they would also do that.”

Hughes pointed out there is a raft of EU laws which have just been implemented by the Scottish Parliament.

“So what happens if the Scottish Parliament says no, we didn’t vote to leave – so we are not repealing those?” she said.

Another potential complication Hughes argued, was that a Legislative Consent Motion – where a devolved administration agrees the UK Parliament can pass legislation on a devolved issue – may be required to deal with overruling EU law in Scotland.

She said: “If they refused, there is a stand-off and the only way round it apart from negotiating would be for Westminster to overrule the Scottish Parliament. But that would be explosive.”

However Jack Montgomery, Scottish spokesman for the Leave.EU campaign said: "Brexit would hand Holyrood a raft of new powers over agriculture, fisheries and aspects of economic policy.

"For Dr Hughes, representing an EU-funded think tank, to suggest that an SNP government would resist these new powers is simply not credible – especially considering the enormous damage Brussels has inflicted on the relevant sectors."

A spokesman for the Scotland Stronger In Europe campaign said: “Looking at the facts and all the circumstances leads to the clear conclusion that the interests of Scotland and the rest of the UK are best served by a vote to stay in the European Union on June 23 – that is what our positive and non-party campaign is working hard to help deliver."

A Scottish Government spokeswoman said Hughes’ report underlined the complexities of the issues that could arise in the event of a vote to leave the EU.

She added: “However, the Scottish Government is committed to making the positive case for Scotland and the UK’s continuing membership of the EU.

“For more than 40 years, individuals, businesses and communities across Scotland have experienced the many social, economic and cultural benefits of EU membership. These include jobs, significant investment, the opportunity for our businesses to trade across the world’s largest single market, social protections like employment rights and the opportunity to work in solidarity with others across the continent to tackle pressing global challenges, such as the movement of refugees and migrants, energy security and climate change.”