NICOLA Sturgeon has failed to ensure a "healthy choice" of candidates to succeed her with the SNP heading for an increasingly ugly contest, according to Scotland's leading academic authority on the party.

Professor James Mitchell, chair of public policy at Edinburgh University, gave his assessment of the first week of the race which has seen bitter infighting.

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Health Secretary Humza Yousaf, Finance Secretary Kate Forbes and former community safety minister Ash Regan have put their hats into the ring to succeed Ms Sturgeon as SNP leader and First Minister with the winner to be declared on March 27.

Professor Mitchell, pictured below, described the line up as "weak" and argued if the party was advancing there would be a bigger selection of senior figures.

The Herald:

He said the limited set of contenders reflected a realisation of tough times ahead for the Scottish Government in terms of delivering domestic policy and for achieving independence.

Professor Mitchell is the author of several books on the SNP including a study of the Hamilton by-election in 1967, won by Winnie Ewing, one of the party's most celebrated figures, and in recent years has become increasingly critical of the party under Ms Sturgeon.

The first week of the race was marked by bad tempered disputes with Ms Forbes, a devout member of the Free Church of Scotland, coming under attack from Mr Yousaf's allies. She faced calls from within the SNP to quit, while some MSPs withdrew their support.

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Ms Forbes in turn raised doubts whether Mr Yousaf - who has faced repeated calls from opposition parties for his resignation over record waiting times in the NHS - would have a confident grip on the nation’s purse strings.

"Leadership contests tell us much about the internal health of a party. They are always challenging, especially when the stakes are high, but this contest has brought tensions, divisions and bitterness to the surface to a greater extent than normal. This week has seen tensions bubbling under the surface emerge very clearly and forcefully," Professor Mitchell told the Herald on Sunday.

"The weak line-up of candidates speaks volumes. If Scotland was on the verge of independence and the SNP was advancing then we would expect senior and experiences figured to be queuing up for the chance to lead Scotland."

He was asked whether Ms Sturgeon - who took over seamlessly from her predecessor Alex Salmond as his former deputy - should have put a better succession plan in place.

"Succession planning in political parties needs to be very different from succession planning in other organisations. While a leader ought to bring on the best talent, ultimately the party makes the choice. The task for the incumbent leader is to ensure that there is a healthy choice from amongst the most talented senior members. This has clearly not happened," he said.

"Nicola Sturgeon appears to have favoured Humza Yousaf from the point when [former Finance Secretary] Derek Mackay’s career self-imploded though was more subtle in lending him support than her predecessor was in anointing her as leader."

He added the apparent preference of Ms Sturgeon - who called Mr Yousaf the night before she announced her resignation but neither Ms Forbes (who was on maternity leave) nor Ms Regan - may have stopped others from standing.

"We have the unusual, perhaps unique, situation in which the candidate to lead a party favoured by the outgoing leader is also the person opposition politicians are very happy to see leading it," he said.

Professor Mitchell warned the contest would likely become nastier

"The bitterness evident in the last week and weaknesses of the candidates will likely be exposed further," he said.

"Each candidate will be wary of criticising Nicola Sturgeon but at some point the SNP will need to face up to some harsh realities – the SNP is no closer to independence today than it was in 2014. It has failed to offer consistent credible answers to the key question and it needs to confront major policy failures," he said.

"The best prospect for an essential honest and open debate, though painful, might be if Kate Forbes stays in the race, confronts these issues knowing that it will not help her win but could contribute to the long-term health of her party. In essence, the SNP needs someone to show leadership even – indeed especially - if that person pays the cost of losing the leadership contest."

An SNP spokeswoman said: “Nicola Sturgeon has been an outstanding leader of the SNP and First Minister for Scotland, winning multiple elections where she offered people across Scotland a better future by giving them a choice to escape Westminster control for good and become an independent country. 

"Over the next few weeks, the SNP leadership contest will show the talent and ideas within our party that can lead us into the final phase of Scotland’s journey towards independence."

Each of the leadership candidates' teams were approached for comment.