NICOLA Sturgeon has denied she and her husband Peter Murrell would wield an unhealthy amount of power over the SNP if she is confirmed as the party's next leader this week.

Sturgeon, who is expected to be named as Alex Salmond's successor unopposed on Wednesday, said she was comfortable with being leader while Murrell is the party's chief executive.

However, some SNP members are uneasy at the prospect, fearing it will put an unprecedented amount of power in the hands of one couple.

Some also worry that, with Sturgeon's mother Joan as the Provost of North Ayrshire Council, it makes the SNP look like a Labour-style "family business" rather than a modernising force.

One senior SNP source said: "Some of us don't really want an alternative Royal Family. We want a new Scotland based on meritocracy."

Another senior party insider said: "It's not ideal, especially looked at from outside. The perception is that it's a bit incestuous, that too much power is in the one household."

Talking to the Sunday Herald, Sturgeon stressed that most of the administrative oversight of the SNP is conducted by business convener Derek Mackay, rather than her husband.

Asked about fears she and Murrell would be an overbearing power couple if she became leader, Sturgeon said: "I've been deputy leader for years while Peter's been chief executive for 10 years. That's not been an issue that's given rise to any concern internally.

"In the constitution of the SNP, the oversight of the administrative side of the party lies with the business convener, not with the leader. So I'm comfortable there are no issues that arise."

According to the SNP constitution, Mackay chairs the main decision-making bodies and runs "operational matters including membership, campaign co-ordination and internal affairs".

However, the constitution also says the leader appoints the business convener each year, putting Mackay's fate in Sturgeon's hands.

The SNP's annual report says Murrell is "responsible for the day-to-day running of SNP activities and projects". However, the party declined to provide his full job description.

Asked if party members could still complain about her if her husband was chief executive, Sturgeon said: "Absolutely. The business convener deals with the internal democracy and the whole oversight of administration. So that gives a route.

"It wouldn't be the chief executive who would deal with a complaint about the leader if I was the leader, it would be the business convener."

Looking back at the referendum, Sturgeon also defended the SNP policy on a currency union, saying it was right to advocate sharing the pound - a policy the Unionist parties blocked - rather than advance a new Scottish currency, as many in the Yes campaign had wanted.

She said: "I think we were in the right position on currency because other positions would have been just as difficult.

"Others take a different view on that. I don't think [a different currency proposal] would have made a fundamental difference.

"By the time we got to the last couple of weeks of the campaign ... currency was not what was stopping people voting Yes in my opinion, there was a multitude of different factors at play. The two things in the latter period were general understandable human anxieties about the unknown and being told we can get something [The Vow] that takes us a long way without all that. Probably that was the most significant factor to those who wanted to vote Yes but didn't."

Sturgeon, 44, and Murrell, 51, were married in Glasgow in 2010 after a seven-year courtship.

Opponents have sought to exploit their relationship to score points in the past. In September 2012, Scottish Labour leader Johann Lamont used First Minister's Questions to ask whether it was right for Sturgeon to get free prescriptions when she lived "in a household with an income of over £200,000 a year".

At the time, Sturgeon earned just over £100,000 as an MSP and minister and Murrell's salary in 2011 was £109,000. It fell to £77,000 in 2012 and was omitted from the SNP accounts in 2013.