The status of European Union (EU) member state overseas territories could "inspire" a special deal for Scotland in the Brexit negotiations, a Holyrood committee has been told.

Professor Dimitry Kochenov, a constitutional law expert, said arrangements for the overseas countries and territories (OCT), which have a range of special relationships with the EU, demonstrate the EU may be prepared to be flexible.

He said: "The EU is actually extremely flexible in the way it extends rights to its own citizens outside of its own territory because EU territory doesn't overlap entirely with the territories of the member states.

"So, we have plenty of examples - in New Caledonia, in French Polynesia, in the Dutch overseas (territories) in the Caribbean, where EU citizens would only have self-employment rights for instance, and no unlimited right to stay otherwise, where EU workers would need to apply for a residence permit.

"If we draw examples from overseas, where the boundaries between full membership and associate membership are quite blurred, we see that the EU is actually ready to go an extra mile to meet the requirements of those territories which are rooted in the special nature of their status, or of their geographical or economical position."

He added: "Something of this kind could theoretically inspire negotiations.

"It will be an uncharted territory in many respects but negotiations that could result in some special relationship between the EU and Scotland, or the EU and, say, Northern Ireland."

Mr Kochenov was giving evidence on EU nationals and their rights to the Scottish Parliament's Culture, Tourism, Europe and External Relations Committee.

The Scottish Government is expected to publish proposals aimed at keeping Scotland in the European single market even if the rest of the UK comes out.

These will include options for a "differentiated deal" for Scotland - something which has been ruled out by the UK Government.

The idea of "associated EU citizenship" has also been suggested. In theory, this would offer British citizens the option of retaining their EU citizenship for a fee.

Professor Eleanor Spaventa, of Durham University, told the committee she could not envisage how associated citizenship, or a Scottish deal allowing freedom of movement to continue, could work.

"It is difficult to understand how you would carve out this deal just for the Scottish people," she told the committee.

"It is impossible - how do you enforce that? If I come here as an Italian to Scotland, how do you ensure that I don't end up in Durham?

"It is okay if I am employed because you are imposing on my employer a visa check, but what if I say that I am self-employed, how are you going to police that?"

Earlier, Prof Kochenov told the committee that "if there is no agreement reached in terms of free movement of persons with the EU, then the quality of British citizenship ... is likely to drop by 30%."

British passports would have the same "quality of nationality" rating as Argentinian passports, he said.

"It is a drastic drop in the quality of the rights that citizens enjoy. All kinds of alarm bells should be ringing."