Image copyright Getty Images Image caption The two sides of the referendum debate disagree over whether Scotland would be able to negotiate its membership from within the EU or have to apply from the outside as a new member

An independent Scotland's entry to the EU would be "relatively smooth and straightforward", an Oxford University professor has said.

The pro-Union campaign has argued that Scotland would be forced to leave the EU and then reapply for membership.

This process could take many years, it has been claimed, with Scotland having to join the "back of the queue".

But Prof Sionaidh Douglas-Scott said it would be possible for Scotland to have uninterrupted membership.

In its White Paper on independence, the Scottish government claimed Scotland would be able to negotiate continued membership of the EU through Article 48 of the Treaty of the European Union.

It has argued that these negotiations could be concluded in time for its target date for independence of 23 March 2016, meaning there would be no break in Scotland's membership.

Rebuffing or alienating a country such as Scotland, that wants to maintain EU membership, and is keen to stress its European credentials, will hardly do much for the EU's image Prof Sionaidh Douglas-Scott, Oxford University

But the UK government and Better Together campaign have argued that Scotland would have to re-apply as a new state under Article 49 of the EU Treaty, which could take several years.

This stance was backed by outgoing European Commission president Jose Manuel Barroso, who told the BBC earlier this year that it would be "extremely difficult, if not impossible" for an independent Scotland to join the European Union.

In a research paper examining how easily Scotland could gain EU membership after independence, Prof Douglas-Scott appeared to echo the Scottish government's position.

Leaving the UK means becoming a new state and going through an accession process to join the EU UK government spokesman

Prof Douglas-Scott is professor of European law and human rights at Oxford, and has written a book on EU constitutional law.

She said: "Despite assertions to the contrary from UK lawyers, EU lawyers and EU officials, any future independent Scotland's EU membership should be assured, and its transition from EU membership (as a) part of the UK, to EU membership (as an) independent Scotland relatively smooth and straightforward."

Proceeding by way of Article 48, as opposed to using Article 49, which would require a full Accession Treaty, would avoid the risk that a newly independent Scotland would be "cast into the wilderness", with its ties with the EU cut on the date of independence, she said.

She continued: "This would be a form of internal enlargement for the EU, and in this way, Scotland's uninterrupted membership of the EU could be preserved.

"It would, however, be necessary for negotiations to commence immediately upon a Yes vote in the independence referendum so that messy contingency arrangements with between the EU and a new Scottish state could be avoided."

What's the difference between Articles 48 and 49?

Image copyright AP

Article 48 - It allows the Treaties of the European Union - the EU rulebook - to be amended by existing members of the European Union, the European Parliament or the European Commission. The members submit a proposal to the European Council and if it - after consulting with the parliament and the commission - decides by a simple majority to look at the proposed amendments, then it is passed on to a "convention". They look at the amendment proposed and, by consensus, adopt a recommendation which is put to a conference of member state representatives for approval.

- It allows the Treaties of the European Union - the EU rulebook - to be amended by existing members of the European Union, the European Parliament or the European Commission. The members submit a proposal to the European Council and if it - after consulting with the parliament and the commission - decides by a simple majority to look at the proposed amendments, then it is passed on to a "convention". They look at the amendment proposed and, by consensus, adopt a recommendation which is put to a conference of member state representatives for approval. Article 49 - The applicant country must apply to the European Council, with the European Parliament and national parliaments also being notified. New conditions and subsequent adjustments to the Treaties need to be agreed between the member states and the applicant state. That agreement is then submitted for ratification by member states.

Prof Douglas-Scott acknowledged that there was no precedent within EU law for a territory of an existing member state becoming independent and wishing to retain EU membership, and the treaties do not provide for such an event.

But she said EU law characteristically takes a "pragmatic and purposive approach" to pressing issues that are not dealt with by specific treaty provisions.

She added: "There was no explicit provision in the treaties capable of dealing with the situation of German unification in the 1990s.

"But the (then) EEC Institutions responded to this event in a pragmatic and expedient manner, enabling a united Germany to become a member of the EU without long drawn out negotiations, accession proceedings or legal wranglings."

'Values and norms'

Prof Douglas-Scott said she took issue with Mr Barroso's assessment that it would be "extremely difficult, if not impossible" for an independent Scotland to join the EU for four main reasons.

She explained: "First, it is inconsistent with previous Commission pronouncements on the issue of Scottish independence. Second, it threatens to cast out Scotland from the EU, thus fracturing the Single Market, ignoring acquired rights and obligations of good faith.

"Third, it ignores the existence and growth of EU citizenship as elucidated in case law of the European Court. Lastly, it is difficult to reconcile with the EU's values and norms as enshrined in the general principles and spirit of the Treaties."

She added: "Rebuffing or alienating a country such as Scotland, that wants to maintain EU membership, and is keen to stress its European credentials, will hardly do much for the EU's image.

"The EU ought to be showing what it can do for its citizens, not rebuffing them."

Responding to Prof Douglas-Scott's paper, a spokesman for the UK government said: "There is no doubt the route into Europe for a separate Scotland would be uncertain and the weight of expert evidence is against the unprecedented use of Article 48.

"Leaving the UK means becoming a new state and going through an accession process to join the EU. The decision on both Scotland's membership would ultimately be for the 28 other member countries of the EU who would need to unanimously agree the terms of that membership.

"A number of influential voices, from the Spanish prime minister to the president of the European Commission, have already made their views on this issue clear. The Scottish government position is, at best, unclear and uncertain."

A spokesman for the Scottish government's External Affairs Minister, Humza Yousaf, welcomed the report, which he said backed the views of many other experts.

He added: "It demolishes the claims of those in the No campaign, who know that the only threat to Scotland's place in Europe comes from Westminster's UKIP agenda and David Cameron's proposed in-out referendum."