Chris Hanlon, who is a member of the party's policy development committee, said the move could help break the current constitutional logjam with First Minister Nicola Sturgeon wanting a new vote and Boris Johnson repeatedly failing to agree.

He said the Prime Minister was more likely to give the go-ahead to a multi-option vote rather than a Yes/No one, as took place in 2014, and it was a position he believed Labour would also find it easier to support.

But pointing to polls showing high public support for devo-max ahead of the 2014 vote, he added that it was "an outrage" that Scots weren't offered that option at the time.

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"We all knew, in fact it was an accepted truism on both sides, that the most popular option for the Scottish people would have been devo-max.

"There were regular reports that such an option, should it appear on the ballot, would receive nearly 80% of the vote.  Neither side wanted that outcome.  SNP leadership wanted nothing less than independence and the anti-independence lobby wanted to preserve the status quo as much as possible," he writes in an article to be published in The National tomorrow.

SNP policy development committee member and former policy chief Chris Hanlon 

"To my mind that’s an outrage. The Sovereign People of Scotland had a clear preference and the way the leadership on both sides of the debate avoided giving it to them was to intentionally not ask them about it."

Hanlon defeated MP Alyn Smith to become the SNP's policy development convener in 2020, but lost the role to Toni Giugliano at the party's internal elections last November.

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He is still a member of the SNP's policy development committee and said he would vote for independence in a multi-option referendum.

"Devo-max isn’t my preference and maybe given the changed circumstances it might not be the choice of the majority of the people of Scotland but part of me remains of the opinion that excluding it from the ballot paper is just plain wrong.

"The people must have the option of choosing the path the largest percentage of them favour," he writes.

The senior activist conceded that while a multi-option referendum may see people vote for devo-max rather than independence, the situation could be a stepping stone to independence.

He said maximum devolution could see a raft of new powers go to Holyrood including over energy and immigration as well as see the parliament gain more financial borrowing powers and over the right to hold an independence referendum itself.

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And he also believed Holyrood could gain the power to sign international treaties, paving the way for Scotland to get a Northern Ireland style Brexit arrangement allowing closer trading ties to the EU.

"It would have to be an STV ballot for a start off.  That risks not getting independence straight away but if that’s what the Scottish people want, that’s what they should get, and I’ll just have to lump it in the short term," he writes.

He told The National: "If Holyrood has an absolute right to bring further referendums to increase its own powers then it is one step at a time, bring in further powers over immigration. The Faroes Islands, though they are not quite independent of Denmark, have devolved powers to negotiate international treaties. They are not technically in the EU."

Ahead of the 2014 vote, the Scottish Government backed a multi-option referendum, including a question on devo-max but that was rejected by the then PM David Cameron who agreed to a Yes/No vote.

Former First Minister Alex Salmond later said he was only putting forward a multi-option referendum as a negotiating tool to get Cameron to agree to what the Scottish Government really wanted, a Yes/No vote.

He told The National in April last year: “In 2011 the idea that David Cameron said, ‘jolly good show Alex, you’ve won the election, and in terms of the rules of cricket it’s your turn to bat and we will now give you a referendum’. That’s not how it happened. 

“What happened is that the week after the election I went down to London to initiate negotiations. 

“Cameron wouldn’t see me, so I started negotiations with [then Chancellor] George Osborne who did his thinking for him and then over the period of months we had to present him with a less palatable alternative than granting a Section 30 [a three-way referendum controlled by the Scottish Parliament]. That’s how it was done.”

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He added: "So, if you want to get a Section 30, the very last thing you do is to tell people that is your aim in the negotiations. David Cameron wouldn’t have granted a Section 30 if we had gone to him and said ‘I’ll tell you what David, what we are wanting is a Section 30, a Yes/No referendum, in which we control the franchise, the timing and the question.

"If I had gone into negotiations saying that I would assure you, we would not have had a referendum in 2014. Therefore, I worry when people say ‘we’ll ask for a Section 30 referendum’. A Section 30 referendum is a tactic, a democratic device, an enabling mechanism, the strategy is Scottish independence, not a Scottish independence referendum.”

Some Scottish Labour figures, including the party's former deputy Alex Rowley, have previously backed a multi-option referendum on the constitution, though the devo-max proposal has not been backed by leader Anas Sarwar.

Last year Kenny MacAskill, the former SNP justice secretary, who is now an Alba MP, advocated Home Rule for Scotland as a compromise.

The life-long independence campaigner said the third option might provide a way to break the “constitutional impasse” in a “deeply divided” nation.

MacAskill, the MP for East Lothian, said he still favoured independence because it would give full control over issues including defence and foreign policy but he added that the country must begin tackling its social problems.

“Something needs to be done to break the logjam and move the country on, as the weekly cycle of ‘we demand it ’and ‘you’re not getting it’ is doing no-one any good,” he wrote in The Scotsman in June.

“There’s work to be done and if there’s ever a moment to think outside the box it’s now. If coronavirus recovery is the issue then powers to address it are required and the status quo is inadequate.

“Building a coalition to expand the powers of the Scottish Parliament without breaking the Union must surely be possible. It also has the benefit of allowing proponents of both absolute positions to see it as a basis for either going forward incrementally or entrenching the foundations more firmly.”

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Scottish Government strategists now believe that the concept of greater devolved powers is too ill-defined and that a truly federal UK would need significant constitutional changes in England. They are therefore unwilling to countenance a third option.

The First Minister told her party conference in November that campaigning for independence would begin "in earnest" this Spring ahead of a new vote by the end of 2023.