NICOLA Sturgeon’s plan for a bespoke Scottish Brexit has been undermined by the head of the European Commission in the UK, heightening the prospect of a second referendum.

Jacqueline Minor said there was little evidence that either the UK government or the other nations of the EU were ready to agree to a “differentiated deal” for Scotland.

The First Minister published a detailed proposal in December on how Scotland might remain in the EU single market after the rest of the UK left in a hard Brexit.

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She admitted the unprecedented idea would be technically and politically challenging and depended on cooperation from the UK government and the other 27 EU nations.

She also said that if her plan was dismissed it was “all but inevitable” that there would be another referendum on independence, given the 62-38 vote in Scotland against Brexit.

However Ms Minor, the outgoing head of representation for the European Commission in the UK, said: "The [Brexit] negotiations will be with the United Kingdom and that means essentially the Westminster Government.

“The first question is will the Westminster Government argue in favour of a differentiated arrangement, and it seems to me that at present they are not suggesting that they will.

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“Should they do so, should they change their mind, then the other members states would have to look at that. I have to say that there is no precedent whereby a free trade agreement has distinguished between significant regions of the partner country."

Ms Minor also said an independent Scotland would have to join a queue of would-be EU members including Montenegro, Serbia and Bosnia and Herzegovina, rather than carry on inside the EU as a continuity state.

Speaking at a Scottish Parliamentary Journalists' Association event in Edinburgh, she said: "Were Scotland to become independent, they would join that list."

However she added it might be easier for Scotland to meet membership criteria such as democracy, rule of law, anti-corruption and protection of minorities than other candidates.

Ms Minor said new members were expected to commit to using the euro as their currency and to reduce their deficit below 3 per cent of GDP - Scotland’s is currently triple that.

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Tory constitution spokesman Adam Tomkins said: "This is a senior figure telling the SNP what it needs to hear. Not only would it join the back of the queue, but we now learn it may have to adopt the euro and tackle an eye-watering deficit. It's time for the Nationalists to be honest about Brexit and stop using it as a tool to agitate for separation."

Scottish Labour's Europe spokesman Lewis Macdonald said: "This is a hugely significant intervention from an experienced and respected official. It's time for the SNP to be honest with voters - an independent Scotland would have to join the queue."

However Scottish Green MSP Ross Greer said: "There are 5m EU citizens living in Scotland, it's unthinkable that they will be told to join the back of a mythical queue.

“What was made clear by this high ranking official was that Scotland already meets much of the requirements needed to continue EU membership as an independent nation.”

AN SNP spokesman said: “Ms Minor’s speech demolished many of the bogus arguments used by the No campaign in 2014 around EU membership.”