Scotland may have to reapply for membership of international organisations such as the U.N. and EU if it votes for independence, according to legal advice published by the British government on Monday.

The rest of the United Kingdom would be a "continuing state" with the same status it currently has in international law if Scotland secedes after a 2014 referendum, two experts said in a legal opinion commissioned by London.

But Scotland would become a "new state" and therefore would not automatically be party to thousands of treaties and membership of bodies also including NATO, the IMF and World Bank, the legal opinion said.

British Prime Minister David Cameron's office said it was taking the "the unusual step of publishing, in full" the 57-page document to clear up uncertainty about the legal status of an independent Scotland.

"If Scotland became independent, only the 'remainder of the U.K.' would automatically continue to exercise the same rights, obligations and powers under international law as the U.K. currently does, and would not have to renegotiate existing treaties or reapply for membership of international organizations," Downing Street said in a statement accompanying the legal opinion.

The opinion by by professors James Crawford of Cambridge University and Alan Boyle of Edinburgh University gives four reasons for its conclusion.

Firstly the majority of cases in recent history worked on similar principles, such as Britain and Ireland in 1922, India in 1947, Singapore and Malaysia in 1965, Bangladesh and Pakistan in 1971, the Soviet Union in 1990 and Sudan and South Sudan in 2011, it said.

Secondly, a majority of population and territory has been an important deciding factor in such cases, and the "continuing" U.K. would have a majority of both population (92 percent) and territory (68 percent), said the legal opinion.

Thirdly Britain's "prominent role in the international order" -- as one of only five permanent United Nations Security Council members, a NATO member, a nuclear weapons state under the Non-Proliferation Treaty and member of the European Union -- meant any change to its status would "cause huge disruption".

Finally the British government has already ruled out agreeing to become a "new state" as well. (AFP)