SCOTLAND'S leading historian has said Nicola Sturgeon has made the "correct decision" to step down as First Minister.

In an exclusive interview with The Herald, Sir Tom Devine, professor emeritus of history at Edinburgh University, described Ms Sturgeon along with her predecessor Alex Salmond as a "giant" of Scottish politics and said both her and Mr Salmond were the most influential leaders since devolution in 1999.

He dismissed claims that the independence cause was now a "busted flush".

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His comments came as Uk government ministers said her resignation represents a “generational setback” for independence, while senior Labour figures say it will help Sir Keir Starmer to secure victory at the next election.

The First Minister announced this morning that she would stand down, saying she had become a polarising figure and no longer had the energy to lead the campaign for independence.

Reacting to the announcement and the potential fall out of Ms Sturgeon's decision, Sir Tom said: "I am being asked if independence is now a busted flush. Only last week a major poll showed a Labour win in the next general election and the SNP becoming the second party at Westminster ahead of the Tories.

"My view is that forces are more important for political change than personalities though they are not unimportant, especially if they are in a leadership capacity.

"It's essential that the SNP obtain a leader with ability and imagination as I think the whole government was beginning to show signs of fatigue. But the alienation from the current Westminster government, in my view, prevails among considerable sections of Scottish society."

He underlined challenges ahead for the independence movement, particularly in how it can secure a new referendum following repeated refusals from the UK Government and after the Supreme Court ruling in November that Holyrood cannot hold a referendum without the consent of the UK Government.

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The historian also raised the prospect that the possible election of a Labour Government in London could dampen independence support. 

"No UK Prime Minister is ever going to make the same mistake as [David] Cameron made in 2012 and agree to a new referendum because it was a close run thing [in 2014]," he said.

"I cannot think of a way round if a future UK leader continues to say no because they now have the legislative backing of the Supreme Court.

"And I think the Labour party will be more acceptable to Scottish opinion than their predecessors. Again...if support for independence does not reach up to the level of 65% in the opinion polls I can't see them conceding as they have the precedent of the Tory government's [refusal]."

Sir Tom, pictured below, said the SNP were at a crucial crossroads and would need to think carefully on who they elected as Ms Sturgeon's successor.The Herald:

"There have been two giants in Scottish politics since 1999. Alex Salmond was one with the breakthrough for the SNP he achieved in 2007. Nicola Sturgeon is the second. I have been scanning a few of the international newspapers today and it is remarkable that the New York Times, the Washington Post, Le Monde and El Pais have given [her resignation] substantial coverage," said Sir Tom.

"One has to remember we are talking about the First Minister of a stateless nation - so that is some impact. It is a remarkable profile and a testimony to the effect she has had.

"She didn't achieve her lifetime aim [of independence] but that I would argue was nothing to do with her inadequacies or abilities and more to do with the anti-democratic position of the Westminster Government and the decision made by the Supreme Court [in November that Holyrood could not hold an independence referendum without Westminster's consent]."

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He added that over the last few months she has shown "real signs of losing her touch" and pointed to domestic challenges over the rising cost and non delivery of two ferries being built at Ferguson's shipyard in Port Glasgow as well as the controversies over her gender recognition reforms and policy on transgender prisoners.

"No political leader is perfect," said Sir Tom.

"What is clear is that up until the last month all the opinion polls have shown sustained figures in support of independence and continuing support for the SNP.

"It's only very recently and for the reasons everyone knows about and that shows I think there was an intellectual and political fatigue beginning to develop. And in that sense, although it came as a surprise, in an historical context she has made the correct decision to go."

Sir Tom voted Yes in 2014 though has since said he is not clear how he would vote in any second independence referendum.

He discussed the forthcoming leadership contest saying his favourite to succeed Ms Sturgeon was Kate Forbes, 32, currently on maternity leave from her role as finance secretary.

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"Perhaps the only mechanism of the whole embroglio of the Scottish Government and the SNP on these recent matters is a fresh hand at the tiller.

"But who is there? My own favourite would be my former graduate student Kate Forbes....Of all the likely candidates...she has considerable intellectual ability and it's quite clear members of the current government and members of the SNP rate her highly," he continued.

"There are of course a number of problems. I am not fully convinced she will want it, there is another issue of her religious and moral convictions which are arguably different from the mood of the current SNP.

"And of course she is relatively inexperienced and young. But I think on the basis of her intellectual track record she would fit the bill."

He added: "There are clear signs of tensions within the SNP than there has been before, that is not to say the First Minister was losing grip which is so vital for a nationalist party, but now she is about to go it will be interesting to see what happens. In terms of the essential role in keeping the party as a disciplined and coherent force while at the same time - which perhaps she didn't do to the same degree - allowing a degree of dissent within the ranks.

"So that the governing ranks in the party show an ability to listen."

In a press conference at Bute House in Edinburgh, where Ms Sturgeon appeared close to tears, she said that while she believed the majority of Scotland backed independence this support “needs to be solidified”.

She added: “To achieve that we must reach across the divide in Scottish politics. And my judgment now is that a new leader will be better able to do this. Someone about whom the mind of almost everyone in the country is not already made up, for better or worse. Someone who is not subject to quite the same polarised opinions, fair or unfair, as I now am.”