European migrants may swing a second referendum in favour of independence, experts believe, if a new vote can be held before Brexit.

In new independent analysis, two international academics re-ignite Scotland's debate on the timing of - and franchise for - Nicola Sturgeon's proposed new plebiscite.

The First Minister this summer signalled a delay in a proposed referendum from just before the UK's exit from the EU to just after - disenfranchising what now looks like a core pro-independence group.

Academics Richard Marsh and Fabian Zuleeg suggest a substantial block of EU nationals will switch to Yes if they get their say - potentially having a huge impact on a close vote.

In an essay for Scottish Centre on European Relations, a think tank, Mr Marsh and Dr Zuleeg calculated that the EU block predicted for 2020 would be big enough to deliver independence if nothing else changed from 2014. "If all EU citizens vote ‘Yes’ to independence, it could have a significant impact: if the 2020 projected number of EU citizens were assumed to have unanimously moved from the No to the Yes cohort in the 2014 referendum, it would have been just enough to switch the result, resulting in a 51% Yes vote."

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Mr Marsh, an economist, and Dr Zuleeg, who is the Brussels-based chief executive of the European Policy Centre, suggest that even a smaller shift in opinion among EU migrant voters would be a potential "game-changer."

They acknowledged that it was difficult to predict how many EU migrants will be in Scotland if and when a second vote is held and how many of those will back Yes.

Foreign nationals eligible to vote, including EU ones, were slightly less likely to support independence in 2014 than the national average, with just under 43 per cent against and just over 57 per cent for. Just reversing those numbers would close the gap between the two sides, as of 2014, by two percentage points, the experts said.

Mr Marsh and Dr Zuleeg wrote: "While there can be no definite predictions, it seems clear that the decision when to exit the EU and when to hold an independence referendum could have a material impact on the outcome, given the potential size of the non-UK EU citizen cohort, which might or might not be eligible to vote in such a referendum. If a second referendum is held before Brexit, EU voters could tip the balance."

Other experts predict that EU voters would turn out for independence in numbers usually only seen in dictatorships. However, this could be offset by pro-Brexit or unionist figures capitalising on the "foreign" vote politically, commentators warned.

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Professor James Mitchell of Edinburgh University said he anticipated a "Gibraltar-scale" show of support for Yes from EU migrants in any second independence referendum.

Some 96% of Gibraltarians backed Remain in 2016 on a huge turnout.

Prof Mitchell said: "These people would be voting to stay in the EU rather than for the idea of Scottish independence itself. I would not expect the result to be 100% but it would be very high.

"This could swing the result if it was a close vote."

"What we are talking about is a small element of electorate - assuming they are allowed to vote - which would want to remain in the EU through voting for independence."

"However, this is a small part of the electorate whose voting could provoke a backlash."

"There may be those who respond by talking of Polish voters 'swamping' the referendum."

Polls have fluctuated on independence ever since last year's Brexit vote. One poll in June suggested No's margin of victory had grown to twenty percentage points, making any EU vote immaterial. Others have been far closer, close enough to make any decision on the franchise crucial. In 2014 the gap was more than 400,000 votes.

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Non-UK EU nationals have the right to vote in Scottish local and parliamentary elections and were allowed to take part in the 2014 referendum. They are denied a vote, however, in general elections and did not have a say in the Brexit referendum of 2016. Analysts believe that EU voters would have changed the result of that plebiscite.

An SNP spokesman said: "EU nationals played an incredibly positive role in the 2014 referendum - and it is only right that everyone in Scotland is given the chance to engage with the democratic process in any future vote on Scotland's future.

"The SNP will work hard to convince everyone, no matter where they are from, of the benefits that independence could bring for everyone in Scotland."