The leader of Scottish Labour is the hardest job in British politics, Anas Sarwar said as he warned leadership contenders against infighting.

Mr Sarwar – who held the title for more than five years – sparked a leadership contest when he was elevated to the House of Lords by Andy Burnham and made a trade minister.

Speaking during a show at the Edinburgh Fringe on Sunday – his first public appearance since quitting as a member of the Scottish Parliament – Mr Sarwar lamented how difficult the party leadership is.

“People talk about the hardest job in British politics, and so often I heard people say the hardest job in British politics was being the leader of the UK Labour Party in opposition,” he said.

“Honestly, hand on heart – because I’ve done it for five years – the hardest job in British politics is being the leader of the Scottish Labour Party.

“And for so many reasons, it is the hardest job in the world.”

Having stepped down as an MSP, Mr Sarwar – who led the party to a disappointing result in May’s Scottish Parliament where Labour dropped to just 17 seats – said he would not be the type of former leader who would be “publicly giving advice all the time”.

“The best thing you can do to support someone in that job is be available to give them advice, be supportive of them,” he said.

“If they ask you to help, always help them; go out of your way to help them but don’t be a public commenter on them.”

Speaking to comedian and podcaster Matt Forde, Mr Sarwar said Scottish Labour had struggled to communicate its vision during the spring campaign, while being hindered by scandals facing the government led by Sir Keir Starmer.

Three MSPs are hoping to replace Mr Sarwar: Michael Marra, Joe Fagan and Monica Lennon, with Ms Lennon yet to secure enough support to get on the ballot of members.

While he declined to endorse a candidate, Mr Sarwar warned the contenders and their teams against infighting as the race becomes more embittered.

“I think genuinely the three people who are standing, I’ve got a lot of time for,” he said.

“I think they are able, talented individuals.

“The only (thing) that I would say to all three of them and to all 17 MSPs is your relationship with each other, your ability to work with each other and to look out for each other is going to be crucial.

“So, yes, go through a full leadership election, but think about what happens the day after it, not just what happens during it.”

Ms Lennon has warned that the leadership race was about finding “our party’s missing soul”.

Writing in the Sunday Mail, Ms Lennon, who is able to return to Holyrood after the summer recess to fill the list MSP vacancy left by Mr Sarwar, said: “Again, our political conversation turns inward as politicians and activists search through the rubble, trying to locate our party’s missing soul.”

She added: “Having lost sight of our roots, we struggle to place ourselves in Scotland’s future.

“It’s the worst of both worlds, but this identity crisis needn’t be the end of our story.

“People still need us, and we need them.”

Despite having been made a lord, Mr Sarwar said he stands by his previous calls for the House of Lords to be replaced with an elected senate of nations and regions.

Mr Sarwar said: “It should be replaced with a democratic chamber of a senate of nations and regions.”

He told the BBC: “I have always said that there should be a senate of the nations and regions. I still have that view.”