A PROMINENT critic of Nicola Sturgeon has given his backing to her Indyref2 route map and said with a strong and united Yes campaign it could lead to Scottish independence.

Jim Sillars, a former SNP deputy leader, spoke out after the First Minister unveiled her long awaited plan to MSPs last week about how she intends to bring about a new vote should Boris Johnson continue to reject an agreement to hold it.

Under the strategy set out last Tuesday, Ms Sturgeon said legislation drawn up by her government had been referred to the Supreme Court by the Lord Advocate to assess whether it was within Holyrood powers.

If so, she said the referendum would take place on 19 October 2023, but if not, the vote would not go ahead and instead the SNP would campaign at the next general election on the single issue: "Should Scotland be an independent country?" She added the event would be a “de facto referendum” on independence.

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The phrase was criticised by Professor James Mitchell, chair in public policy at Edinburgh University, and a leading expert on the SNP, who said there was “no such thing as a de facto referendum” and that elections and referendums “are quite distinct”.

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He told ITV Border: “It’s not for a political party to dictate the terms of an election. In a referendum the question is very clear and that’s the whole point of a referendum — it’s focused. There isn’t the same focus in an election. An election is simply not a referendum, a de facto referendum or any other kind of referendum.” Ms Sturgeon said on Friday this issue is a "matter of real politics, not abstract academic arguments".

Speaking to the Herald on Sunday, Mr Sillars was not hopeful the bill would be found to be within Holyrood's powers though was optimistic about the Westminster plan. He suggested Ms Sturgeon's use of the term "de facto referendum" was a misstep.

However, he said it was "rubbish" to say parties could not use elections to campaign on single issues, referring to the 2019 poll when the Conservatives campaigned to "Get Brexit Done" and the February 1974 election which the Tories fought on the issue "Who Governs Britain?" following a series of industrial disputes.

"According to Nicola we are going for the 2024 election. I regret the use of the term "de facto referendum". I don't think that is necessary or indeed accurate.

"It has always been the case and it has always been recognised that if Scotland voted for independence in a Westminster election then independence would have to be conceded," he said referring to a statement by former Prime Minister Margaret Thatcher.

"But things have changed in the constitutional mind over the years as referenda have become part of the constitutional architecture. People now look to votes as well as seats.

"So I think what should be the case in 2024 is [there to be] an unambiguous opening statement in the manifesto that we are inviting people to vote for the Scottish National Party on the basis that your vote will be for independence and to negotiate independence. It will be an independence election."

He added: "People who are saying you cannot have a single issue Westminster election are talking rubbish. I use that term advisedly. What about the 2019 Westminster election "Get Brexit Done"? And if you go back to the February 1974 election [former Conservative PM] Ted Heath called an election on the single issue of "Who Governs the country, the government or the trade unions? It is not unusual to have a major dominating issue in a general election."

Mr Sillars went on to argue it was a realistic goal for the SNP to win more than 50 per cent of the votes though warned it would need a vigorous campaign for independence by the party.

Put to him that such a goal was "very challenging", he said: "No, it's not difficult if we campaign."

He added: "The SNP has not campaigned for independence and at the Holyrood election Nicola Sturgeon was quite specific in saying 'this is not about independence'. I have argued we should be campaigning to get up to 60 per cent support for independence.

"First, if we get to that stage its such a statement it could not be ignored by anyone in London.

"Second, is that if we are going to win independence and make it work properly we have to have the acquiescence of those who were defeated.

"And if you're at 60 per cent those at 40 per cent, reluctant though they may be, would have to accept that that is the will of the majority. And therefore an independent Scotland would more easily become a united Scotland. It wouldn't be necessary but it would be wise to get the highest vote possible."

He added: "We have time on our hands and in order to unite the independence movement which in some sections has splintered at the present time, we need a bit of statesmanship from Nicola Sturgeon to unite the movement and help create a national organisation that will campaign."

Mr Sillars said it would mean the SNP should bring into "their tent other people" not in the party who could help make and build the case for independence.

"The SNP cannot on its own win a referendum or a general election [on independence]. On the basis of seats and votes we have to embrace talent outside the ranks of the SNP," he added.

"There is a huge amount of policy work required to... address the thorny questions that are going to be asked of the independence movement - on debt, on currency, on Faslane, on security, on our position on Nato - and these at the moment, as far as I can make out, our not thought out."

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He went on to point out that both Levelling up Secretary Michael Gove and Scottish Secretary Alister Jack had both said that 60 per cent support for a referendum could not be overlooked.

"If we get 60 per cent in favour of independence, ipso facto, it's 60 per cent also in favour of a referendum," he said.

"We live in a democratic society and for all the criticism that one might make of the Westminster parties they are democratic. It is inconceivable that if there is 60 per cent support for independence by the time we reach May 2024 and that becomes manifesto in the actual [election] results I would expect democrats to understand the democratic message."

Mr Sillars, a former SNP MP, has been highly outspoken in his criticism of Ms Sturgeon in recent years and even donated to Scottish Labour's campaign to hold onto the Dumbarton seat at last year's Holyrood election.

His backing comes just weeks after he renewed an attack on Ms Sturgeon saying there was “no point” in a second independence referendum at present as the Yes side is unprepared and lacking in support.

In a letter to the Herald, Mr Sillars said a “rock solid support for independence” of 60 per cent was needed before the Yes side would be in a position to win.

Dennis Canavan, who chaired the Yes campaign in 2014, also backed Ms Sturgeon's route map.

The former Labour MP and independent MSP said there was "an element of risk" in the First Minister's plans but that sometimes such a strategy had to be advanced.

"The First Minister is quite right to emphasise that she wants a lawful referendum and she hopes that the Supreme Court will clarify whether her draft bill for a consultative referendum is within the legislative competence of the Scottish Parliament," he told the Herald on Sunday.

"However, there are three possible outcomes of such Court action. The Court may decide whether or not the draft bill is within the competence of the Scottish Parliament. But the Court may decline to decide on the matter of competence on the grounds that it will not take a view on a draft bill because it is only a "draft" and therefore a hypothetical question. Such an outcome would obviously not give the clarification which the First Minister seeks."

He added: "There is an element of risk in the Scottish Government's route map to independence but sometimes politicians have to take calculated risks for a good cause.

"It will ultimately require political action rather than just legal action to hold a successful, lawful referendum. The First Minister is correct in stating that the democratic rights of the people of Scotland are paramount.

"If Boris Johnson continues his intransigent refusal to let the people decide by means of a lawful referendum, then an increasing number of people may feel that they have no alternative but to use the next General Election to send out a strong pro-independence message.

"To address Professor Jim Mitchell's point,the message could be more focused and therefore more powerful if a brief pro-independence wording were included in the description under the candidate's name on the ballot paper.

"However, if such a project is to be successful, the people need to be mobilised well in advance and that means organising an inclusive, comprehensive campaign to win the hearts and minds of the people, especially those who are undecided."