A claim that it may be "difficult, if not impossible" for an independent Scotland to join the European Union appears to have had little effect on the outcome of the referendum, a poll suggests.

European Commission president Jose Manuel Barroso's warning has tipped just as many voters towards a Yes vote than it did a No vote, with around 21% swaying each way and cancelling each other out and the remaining voters saying it made no difference.

Better Together said Mr Barroso had knocked the "wheels off the independence wagon" with his claim, but the Scottish Government said it was "preposterous" and predicted it would boost support for independence.

Nearly two-thirds (63%) of all voters would want a referendum on an independent Scotland's EU membership, against 23% who do not, according to the Survation poll of 1,005 people for the Scottish Daily Mail.

But Scots are also more supportive of the UK as a whole staying in the EU, with nearly half (49%) backing ongoing EU membership and around a third (35%) backing an EU exit.

Survation said: "It seems that, for the 35% of Scottish people who would vote to leave the EU, the notion that an independent Scotland might be barred from rejoining may be attractive rather than worrying."

More people think Scotland would have to join the EU like any other country (45%) than those who think the Scottish Government's claim of continuing membership will be the likely outcome (34%).

Scottish candidates from the UK Independence Party (Ukip) will launch their European Parliament election campaign in Glasgow on Sunday in the hope of convincing voters to back their vision of a United Kingdom outside of Europe.

A spokesman said: "As Scottish opinion polls predict Ukip winning at least one seat, David Coburn, lead candidate, and his team will be outlining the issues Ukip will campaign on and our vision of Scotland at the heart of a United Kingdom freed from the shackles of the European Union."

SNP deputy leader Nicola Sturgeon said: "In recent days, a wide range of European experts have said that Mr Barroso was very wrong to compare Scotland's position with that of Kosovo, including former EC director general Jim Currie, who said that 'everyone would recognise Scotland would have the right to become a full blown member' of the EU.

"We have been an integral part of the EU for over 40 years, and will continue to be so as an independent member state - but with a direct voice and votes to protect Scotland's national interests."

The poll also found that 53.9% of respondents believe David Cameron should hold a public debate with Alex Salmond.

Both the Prime Minister and First Minister are due to hold separate Cabinet meetings in the north-east on Monday.

Ms Sturgeon added: "Mr Cameron is going to be very near Alex Salmond on Monday when the UK and Scottish Government cabinets both meet in the north-east. Instead of controlling the No campaign behind the scenes, the Prime Minister should find some courage and take part in a public debate with the First Minister."

Yesterday's Survation/Scottish Daily Mail poll revealed that those who would vote No to Scottish independence are greater than those who would vote Yes, by nine points (47% to 38%) if the referendum were held tomorrow.