The UK and Scottish governments should make public their legal advice on the "vexed" issue of an independent Scotland's membership of the European Union.

Traditionally governments do not disclose legal advice they have received but Bruce Beveridge, president of the Law Society of Scotland, argued that such information would "help provide clarity for voters".

The society has published a discussion paper on what it says are key questions which need answers.

As well as calling for the Holyrood and Westminster administrations to publish their legal advice on European Union membership, the society wants those opposed to independence to set out what a No vote in next year's referendum could mean in terms of further devolution.

Mr Beveridge said: "There are many questions to be answered before September 2014, answers which would allow all of us to make a more informed decision about our future; from how our Parliament should be structured, the currency we would use, what level of tax we would pay, to cross-border treaties and our relationship with other countries in Europe and around the globe."

On EU membership, the paper stresses the "need for legal certainty" when people vote in the referendum.

While the Scottish Government has said it will seek to negotiate membership of the EU on similar terms to those it has within the UK, others claim that an independent Scotland would need to apply for membership and may not be able to secure the same opt-outs on issues such as currency.

"Both sides of the argument will need to clarify as much as possible those issues where there is currently contention," the Law Society paper states.

It calls on the SNP administration to set out what would happen if negotiations about EU membership could not be concluded in the 16-month window period between a Yes vote in the referendum and "Independence Day", the date on which Scotland would become an independent nation.

"Would Independence Day be moved back to allow for a conclusion to negotiations or would Independence Day be a fixed date requiring Scotland to leave the EU and rejoin when the negotiations were concluded?" the paper asks.

The UK Government is urged to say whether it would support an application by an independent Scotland to join the EU.

Mr Beveridge said: "Membership of the European Union continues to be a vexed question. We think people should have more information about an independent Scotland's future membership of the EU and, while acknowledging the right of government not to disclose legal advice received, we think both the Scottish and UK governments should publish the law officer legal advice they have been given to help provide clarity for voters."

The society would "not take a view either for or against independence" but said the debate in the run-up to the September 18 vote should be "reasoned, informed, informative and respectful".

On currency, the society paper says that the Scottish Government should set out the contingency plans if the UK Government does not agree to the SNP's preferred option for an independent Scotland to keep the pound in a formal currency union with the rest of the UK.

It also argues that Labour, the Tories and Liberal Democrats should set out their proposals for further devolution in the event of a No vote.

"As much as people in Scotland deserve to know the consequences of a Yes vote in the referendum, we believe the electorate deserve to know as far as possible the consequences of a No vote."

The society says it wants to know what further powers each of the parties proposes transferring to Holyrood, what the time-scale for this would be and if Labour, the Conservatives and Lib Dems are prepared to agree a joint programme on this.

Mr Beveridge said: "There will be many who want Scotland to remain part of the UK but are still keen to know if a No vote means retaining the status quo or if there will be opportunity for change. The pro-Union parties should be providing information at this stage about the potential for further devolution of powers from Westminster and how the parties would form a consensus to allow these to be delivered."

A Scotland Office spokesman said: "We have already published the legal opinion of eminent experts making clear that an independent Scotland would have to apply for membership of the EU and other international organisations, and subsequent Scotland Analysis papers have made clear the complications it would face on issues such as currency.

"A number of the questions relate to areas which would be subject to negotiation should the people of Scotland vote to leave the UK for good. There is no doubt independence would mean a huge number of complex and irreversible changes to life in Scotland."

Deputy First Minister Nicola Sturgeon said: "This paper makes clear that whichever interpretation is taken of the EU treaties, Scotland already conforms to the EU's requirements and qualifies for EU membership as well as membership of other international institutions in its own right.

"That is a the common sense position that we have set out and which is supported by a number of eminent experts in EU affairs. It would be counter to the entire ethos of the EU to seek to remove a country from the EU which wishes to remain within it and which already complies with EU laws.

"As the Law Society will be aware we have already published a series of detailed papers and statements on key questions which show both how and why an independent Scotland would keep the pound; set out our proposals for a written constitution; and demonstrate the economic and financial strength of Scotland. We have also made clear that our White Paper will be entirely consistent with our legal advice on the issue of European membership."

SNP MSP Annabelle Ewing said: "Scotland has a successful and independent legal system. No doubt if we didn't, and it was suggested we develop one now, there would be the same denigration of that idea as Project Fear direct at an independent Scotland.

"The Yes campaign is rightly answering people's questions about what an independent Scotland will look like, and we are delighted to outline the gains that a Yes vote will bring next year, but many of these questions can equally be levelled at the No campaign, as this report indicates.

"We hear many empty promises about more powers in return for a No vote, but the No campaign promised Scots a 'better form of devolution' in return for a No vote in 1979, but all we got was 18 years of a Tory government which we didn't vote for."