SCOTLAND needs to hold a second independence referendum by the summer of 2017 if it wants to remain in the EU, a former senior adviser to the European Commission has warned MSPs.

Dr Kirsty Hughes told the Scottish Parliament’s European and External Relations Committee that Brussels was already considering putting Scotland into a “transitional holding pen”, to avoid the country being taken out of the EU and then having to apply to come back in.

The adviser warned the politicians that if Scotland is to remain in the EU then it will be on the EU’s terms, which could mean taking the euro. Dr Hughes, now an associate fellow of the Friends of Europe think tank, told MSPs independence would be the “simplest and most obvious way” to stay in Europe.

“I talk to people in Brussels, off the record, who are talking about Scotland being in some sort of transitional holding pen. It wouldn’t have a seat in the Council of Ministers until ratification of the treaties, but it wouldn’t have to go through an absurd out and then in process.

“I go through all that for now because I think there is a timing issue. If Scotland waits until nearly the end of the two years to say, ‘This isn’t okay and now we’re having an independence referendum’, you might not have had that and had time to have the negotiations with the rest of the UK on dissolving the Union before the whole of the UK has left. So, it’s obviously a very big political judgement about whether and when to call an independence referendum.

“If it was only a question of logic, you would call it as soon as possible in my view. You would call it, anyway, let’s say, by next summer because then you would have actually had the dissolution talks – if it was successful – with the UK before the UK left.

“That would make it much easier for the EU to get into some of these transitional holding pen arrangements than otherwise.”

However, she added: “The EU does not want a mini-UK back in the EU if the rest of the UK is leaving. In other words, it does not want the awkward squad member in a smaller form.

“So if the idea of a successor state is that you want the opt-outs from the euro, the budget rebate, the opt-in deal on justice and home affairs, I don’t think that will be forthcoming.”

The committee also discussed the theory that Scotland does “a reverse Greenland”, where Greenland left the EU but remained part of the Kingdom of Denmark.

However, Professor Drew Scott from the University of Edinburgh, who has also advised the European Commission, said this could cause difficulty with cross-border trade between Scotland and England.

“You would have to set up a whole bunch of arrangements to ensure that English goods ... didn’t enter the EU via a free trade corridor that Scotland enjoyed with the EU,” he said.

Professor Sir David Edward, a former judge at the European Court of Justice, said those imagining “a free-floating Scotland” in the EU and the UK “cannot ignore geography”.

“It’s fine talking about Greenland but Scotland isn’t even remotely Greenland,” he said. “It’s connected by its navel to England, and you have to start from that rather simple fact.”

Earlier, External Affairs Secretary Fiona Hyslop had told the committee that the UK Government “should think carefully about when and how they lodge Article 50” and trigger the two-year process to leave.

She added: “I have absolutely, hand on heart, no idea where the UK Government is coming from and what they are trying to achieve and we might not even know that until September.

“My worry is if they move quickly for Article 50 lodging, either now or indeed at the point of a new leader coming in, if we’re not in before that making sure our voice is heard and that we get a chance to express our views, it will be very difficult afterwards.”