WILLIE Rennie has cast doubt on whether an SNP majority in the next Holyrood parliament would be a "legitimate" mandate for a second independence referendum.

The Scottish Liberal Democrat leader said there were "many factors" to a mandate, including the conduct of the election campaign, not simply parliamentary arithmetic.

He said there would be a "stramash" of competing arguments after May 6 if the SNP emerged with more than half the MSPs, and it would be for Boris Johnson to evaluate them.

In an election interview with The Herald, he explained: "Was it a valid, was it a clear result? Did Alex Salmond rig it? Is it the right time? All of those debates will go on, I'm sure.

"The Conservative government at Westminster will have to decide what they want to do."

Asked if a mandate was simply a question of MSP numbers, Mr Rennie, who helped lead the Better Together campaign in 2014, disagreed.

He said: "It's how it's done, isn't it?

It's how clear. Because Nicola [Sturgeon] changes her message from time to time. She says, What you're doing is electing me to lead the country.

"She doesn't put it [Indyref2] in her election address that goes through every door.

"I'm not saying she's ignoring it. Everybody knows they stand for independence.

"But they know they put the foot on the gas and take it off from time to time.

"So they're not always pushing it constantly. So it all depends on how the election is run and all that kind of stuff as to how legitimate it is."

Mr Rennie also said the next Scottish Parliament could "build the foundations" for a return of the Labour-Liberal Democrat coalition that ruled at the outset of devolution.

The North East Fife MSP said he and Scottish Labour leader Anas Sarwar "clearly get on well together", and agreed that economic recovery was the priority, not independence.

He said: "Labour and ourselves have got a tradition of working in partnership. There's a close alignment over time between our two parties.

"We've got different heritages. We appeal to different people in different parts of the country.

"There's a distinct identity for each party. But I think the potential is there for us to work together in the future."

Discussing the possible return to the Labour-LibDem alliance that preceded the SNP coming to office in 2007, he said: "You need to build the foundations for that now if that's going to happen. I think we've started off on a path that's encouraging.

"A lot might change along that route, there may be other events that come along, but I like to hunt for agreement with other parties where we can.

"What form that is, I don't know. But I would like to see the progressive, pro-UK side gain in strength and I think we're part of that, and I think Labour are part of that."

He said voters were "sick to the back teeth" of the anger and division in Scottish political debate, and he offered a "gentler kind of politics" and Mr Sarwar appeared to as well.

He went on: "Who knows where it goes? But I know that for Scotland to be in a better place longer term, we need the progressive pro-UK forces to be stronger."

Mr Rennie, who goes into his second Holyrood election as leader with five MSPs, said he expected to improve the party's tally next month, with the West, South and Glasgow regional lists being targeted more efficiently than in past campaigns.

The party is also hopeful of gaining the Caithness, Sutherland and Ross constituency from the SNP.

Mr Rennie said his party's support was "solid", however the SNP's was "softer than I've ever seen it".

He said Ms Sturgeon appeared to be struggling to get "traction" in a campaign that was subdued as a result of the pandemic, but also because of specific problems for her party.

He said: "There's a lack of enthusiasm [among SNP voters], the Alex Salmond stuff has poisoned things a bit, all the arguments, it's taken the shine off things.

"It's just made them feel as if the project is not as clean as it was. And pushing independence in the wake of a pandemic is definitely jarring."

But his harshest words were for the Tories under Douglas Ross, whom he accused of fostering anger and division in Scottish politics.

He said: "They're not reaching out to win people over from the SNP, they've not got the slightest bit of interest in getting that.

"All they're trying to do is beat Labour into second place.

"That is depressing. Surely you've got to have parties that are aspiring to something more than that? Let's make a positive case for change."