POLLING expert John Curtice has delivered his verdict on where Humza Yousaf quitting leaves the SNP – and what challenges await the next leader.

The Strathclyde University political scientist told The National the opposition had been “too successful” in getting rid of the First Minister.

He said: “You don’t want to do that if you’re in opposition and the guy in front of you is not very good. You want to keep him hanging on a thread.”

Curtice further said that Yousaf had been “relatively unpopular, relatively weak” and this had actually  benefitted both Labour and the Tories.

The polling guru said that a partnership between SNP Westminster leader Stephen Flynn (below) and leadership favourite John Swinney could be “something like what’s required” if the party were to keep their place as the third largest party in Westminster after the General Election.

The National: Stephen Flynn

But he expressed doubts about Swinney’s ability, saying: “Does John still have enough fire left in the belly to go right back to the frontline and take on a role that he certainly struggled with 20 years ago – and will he do any better second time around?”

He said anyone taking on the leadership now would face an uphill struggle “because of the state of public services” and the “small matter of the police investigation”.

READ MORE: John Swinney 'giving active consideration' to calls for him to step in as SNP leader

And Curtice further set out the “job spec” for any hopeful future first minister.

He said: “One is to unite not only the SNP but also get the Greens back on board in some way or another, while still keeping Fergus Ewing quieter than he’s been in the recent past.

“Point two is you need someone who can reach out to the wider public, persuade them that the Scottish Government’s doing a decent job, can campaign effectively etcetera.

“Swinney can probably do the first job but I’m not sure he could do the second and it’s just a case of ‘back to the future’.

“Kate Forbes [below] can probably do the second job but the question is: can she do the first?

"The other characters are essentially unknowns.”

The National: Kate Forbes

On Swinney’s ability to connect with the public, Curtice added: “Swinney’s expertise, I think, is being able to say nothing for three minutes. Definitely who you want as your deputy but it’s not the person to front an election campaign.”

He was scathing about Yousaf’s press conference on Monday, saying the speech was “terrible”.

He added: “It was very self-regarding. Theresa May could do a better job.”

But Curtice added that Yousaf had been partly correct to say that independence felt “frustratingly close”.

The political expert said: “It is in the sense that 50% of people are in favour of it but there’s no chance of a referendum in the near future.”

A spokesperson for the First Minister hit back at Curtice's comments, saying: "That's unnecessarily churlish. It was a statement that showed the mark and quality of the man.

"Perhaps John could conduct an opinion poll to see whether the public share his view."