Mr Salmond, 45, has unexpectedly announced his resignation at the party's annual conference in September after 10 years as national convener.

Sir Sean, who supports the SNP financially and has campaigned alongside Mr Salmond, told BBC News Online Scotland: "He has been great for the party and I look forward to seeing what comes next."

An MP and Member of the Scottish Parliament, Mr Salmond's leadership style has been criticised from within the party in recent years.

It has been a rare privilege to lead the SNP over the last decade

Alex Salmond

Most recently, Mr Salmond was at the centre of the controversy over the suspension of Ian Blackford as party treasurer, who threatened to sue him for defamation.

Speaking at a news conference in Aberdeen, he revealed that he had only reached his decision at the weekend. He said that 10 years into the job seemed "an appropriate time" to reflect on the position.

"I think 10 years has been the allotted term of SNP leaders," he said, pointing out that his predecessor, Gordon Wilson, had served the same length of time in the top job.

Asked for his preferred successor, he said: "I have got my own private thoughts but obviously they are private."

'Complete puzzle'

BBC political correspondent Nick Robinson described the resignation as "a complete puzzle".

"Why if it was always going to be 10 years, hadn't we known about it. The decision seems to be very last-minute," he said.

In a letter to SNP members, he said: "The party is now at its strongest position ever.

Facing the media in Aberdeen

"We are the official opposition in the Scots Parliament, we have over 200 local councillors, we lead the Scottish opinion polls and are at over 30% in the Westminster polls.

"I am absolutely convinced that the SNP will win the next Scottish election and take Scotland forward to independence.

"However, translating that political success onto a personal level, that would effectively lock me into a further decade as party leader.

"It has been a rare privilege to lead the SNP over the last decade. I have enjoyed myself enormously. I have no complaints and no regrets."

Blackford turmoil

He said he had "no intention" of giving up politics and planned to continue as MP and MSP for Banff and Buchan, in the north-east of Scotland.

As an indication that he did not intend to fade away from SNP politics, Mr Salmond added: "I hope to serve Scotland in the future in some other capacity."

The battle for the job has begun with left-winger Alex Neil confirming his intention to stand. He is likely to face competition from deputy leader, John Swinney, who will announce a decision in the next few days.

In full flight at a party conference

Other names in the frame so far are deputy leader, acting treasurer Kenny MacAskill; justice spokeswoman Roseanna Cunningham and business manager Mike Russell.

Political opponents seized on the Ian Blackford turmoil. Liberal Democrat MP Menzies Campbell said: "It makes no sense whatsoever for Alex Salmond and his treasurer to be fighting each other like ferrets in a sack."

Enterprise Minister Henry McLeish, a Labour MSP, said: "The SNP is a single-issue protest group who use the luxury of knowing they will never be in government to come up with crazy and uncosted promises to the people of Scotland."

Economic background

In March, members of the party's national council approved the policy of an independence referendum being held by an SNP-led Scottish Parliament or by the Scottish Parliament, if the SNP won a Westminster election.

Mr Salmond was an economist with the Royal Bank of Scotland before winning the Banff and Buchan Westminster constituency from the Tories in 1987.

The following year he interrupted the chancellor's Budget speech in protest at the introduction of the poll tax in Scotland. He was thrown out of the chamber for a week.