NICOLA Sturgeon should declare independence if the UK votes to leave the EU but Scots back staying in, a former SNP leader has said.

Gordon Wilson said the First Minister would have a mandate to break up the UK if she announced her plan in advance.

David Cameron has promised an in-out referendum on the UK's membership of the EU if the Conservatives are in a position to deliver one after the General Election.

Ms Sturgeon has said the prospect of Scotland leaving the EU against its will could create the conditions for a fresh independence referendum.

Former MP Mr Wilson who led the Nationalists throughout the 1980s, will set out his proposal in a new "strategy for independence" to be published under the auspices of his Options for Scotland think tank today (Tues).

It says: "If the Tories win, as is feasible, then the UK will be faced with an in-out referendum on the EU.

"This will be decided on English votes given the disparity in populations amongst the component units of the United Kingdom.

"If that vote is to leave the EU, then provided the SNP has campaigned for a mandate, the Scottish Government will have a democratic majority to retain membership the EU through a declaration of independence."

The strategy says an independence referendum could still be held if "politically desirable".

It says the pro-independence side would win as the economic arguments in favour of remaining part of the EU would be overwhelming.

Mr Wilson will also call for an "independence convention" of pro-independence groups to be established on September 19, the anniversary of the referendum result, to maintain pressure to leave the UK.