Legal advice commissioned by a pro-independence group has suggested there are "good arguments" to be made for holding a second referendum without UK Government approval.

Forward As One had set up a crowdfunder to instruct counsel to explore a possible legal challenge to Boris Johnson's refusal of a Section 30 request by the Scottish Government to stage a vote.

In his opinion, Aidan O'Neill QC of law firm Balfour and Manson said the Scotland Act could allow for the Scottish Parliament to legislate for another independence referendum - however he said his conclusion would need to be tested in court.

The document, paid for by the group after raising £40,000, said MPs or MSPs could seek a "declarator" from the Court of Session on the issue.

Mr O'Neill wrote: "I consider there to be good arguments to the effect that the Scottish Parliament have the power, under the provisions of the Scotland Act 1998 as they currently stand, to legislate for the holding of a referendum on Scottish independence.

"The matter has never been the subject of authoritative legal decision and is not, however, free from academic controversy (and it is reasonably anticipated that this conclusion would be disputed by the UK Government).

"It is in principle open - even before any such legislation is laid before or passed by the Scottish Parliament - for persons with recognised legal standing (which would include, in these circumstances, individual MSPs and MPs) to seek a declarator from the Court of Session on the issue of whether the Scottish Parliament already has the power to legislate for the holding of a referendum on Scottish independence."

The opinion also states that, regardless of the outcome, a court action will "provide legal clarity in which political decisions can be made and in so doing ensure the clearer and proper working of the UK constitution".

First Minister Nicola Sturgeon has repeatedly insisted the Scottish Government would seek the powers from Westminster to hold another referendum in a way that is above legal challenge.

However, some in her party have called for a referendum to be held within the power of the Scottish Parliament, or even to begin negotiations for independence after a win for the SNP at the Westminster election - which was dubbed Plan B and rejected by party members at its autumn conference.

The Prime Minister this week rejected the First Minister's request for powers to be handed to Holyrood to hold a second vote - a decision Ms Sturgeon condemned as an affront to democracy.

Following publication of the legal advice, a spokesman for Ms Sturgeon said: "First and foremost this is an issue of democracy and respecting democracy. Respecting people's votes in elections.

"Ultimately this has to be settled by respecting democracy, respecting election results, and the position the UK Government are taking, we believe, is pretty unsustainable.

"The onus shouldn't be on us to come up with a Plan B or a Plan C or a Plan Z, there is a perfectly well understood political and democratic precedent for how this is done, and that is the basis on which we published in December, following the precedent of 2014.

"We shouldn't have to look for all sorts of alternative plans when there is a perfectly good one in front of us."