Scotland would not continue to hold the same rights and powers in the event of a yes vote in the 2014 referendum, legal experts have suggested.
Professors James Crawford and Alan Boyle said that an independent Scotland would have to renegotiate its relationship with international bodies.
Their views are contained in a UK government document setting out the case for keeping the UK intact.
The Scottish government said the legal opinion was "helpful".
Deputy First Minister Nicola Sturgeon believed the views appeared to "back up" the Scottish government's position.
The UK government said the legal opinion showed:
- An independent Scotland would be regarded as a completely separate state under international law, with the continuing UK retaining responsibility for all UK institutions, laws and treaties.
- An independent Scotland would become a "successor state", rejecting the SNP government's argument that Scotland and the UK would be regarded as two new states.
- A newly independent Scottish state would have to negotiate with the UK government on issues like a currency union, financial regulation and national security and would have to hold talks with the European Union to agree new terms and conditions.
- In the event of a vote for independence, the UK, as a "continuing state" would not have to negotiate new international treaties or memberships.
Prof Crawford told BBC Radio Scotland's Good Morning Scotland programme: "In all but one or two cases, the remaining state has continued - the existence of the predecessor - the new state has broken away and has had to start with negotiations from scratch."
He said Serbia and Montenegro; Pakistan and India, Bangladesh and Pakistan and the Soviet Union were all examples of the existing state "maintaining continuity" following change.
Mr Crawford added that membership of international organisations would not come automatically for the new state.
He explained: "The cases of separation since 1994 have followed the same pattern - South Sudan and Sudan to take one example; Eritrea and Ethiopia to take another. So the dominant pattern is the breakaway state has to begin by applying for admission to the UN and in the case of the EU it would be the EU as well."
The legal expert from Cambridge University insisted he was not suggesting that the negotiations would be difficult, in most cases.
He explained: "EU membership will come as a matter of negotiation, UN membership will be straight forward but in the case of the EU there will be things to negotiate such as the British opt-out and so on, financial contributions, and they are not automatic."
Ms Sturgeon said in response to the legal document: "James Crawford has said the Scottish government's timescale for independence negotiations is realistic, the treaty accession would not be a problem and that EU membership wouldn't be difficult.
"That seems to me to back up the Scottish government's position.
"I'm not sure that's what the UK government intended, but it's quite helpful."
UK Advocate General Lord Wallace - a former deputy first minister of Scotland, said: "The legal advice is clear. In the event of independence, the remainder of the UK would continue as before, and Scotland would form a new, separate state."