Richard Leonard has insisted he will lead Scottish Labour in next year’s Holyrood election campaign, despite mounting calls for him to quit.

Mr Leonard criticised “disgruntled MSPs” who are now demanding he resign – with James Kelly, Daniel Johnson and Jenny Marra all publicly speaking out against their leader.

Mr Kelly quit as the party’s justice spokesman at Holyrood, with his resignation letter claiming it is in Labour’s “best interests” for Mr Leonard to stand down.

But Mr Leonard insisted: “I am leading Scottish Labour into the 2021 elections on a platform of building a National Care Service, establishing a quality Jobs Guarantee Scheme and reviving Scotland’s economy with a Green New Deal.

“If any party representative thinks an internal faction fight is more important than this agenda, they will have to answer to the party members and the voters whom we serve.”

Mr Leonard added it was “deeply disappointing that disgruntled MSPs who never supported my leadership” were now trying to “wage an internal war”.

Glasgow MSP Mr Kelly revealed he had already told Mr Leonard privately that he believes if Labour is to reverse its fortunes in Scotland, “Richard must stand down”.

Meanwhile, North East Scotland MSP Jenny Marra told the Times newspaper that if the party does “not change course now, we risk catastrophe”.

Their calls were backed by fellow MSP Daniel Johnson, who said: “It is not easy speaking out but my colleagues Jenny Marra and James Kelly have done the right thing.

“It is time to recognise the situation we are in and for Richard to step down.”

Former Scottish Labour MP MP Ged Killen added his voice to the calls, saying while Mr Leonard was an “honest, decent man”, under his leadership “things have gone from bad to significantly worse”.

Mr Killen, who lost his Westminster seat in December, added: “Every party member I speak to is in despair. He must now do the decent thing and resign.”

Labour is currently third in the opinion polls in Scotland, behind both the SNP and the Tories.

In the European elections in May 2019 the party slumped to fifth north of the border, polling less than 10% of the vote.

With MSPs facing another Holyrood election next May, concerns have been raised about Mr Leonard’s leadership.

Mr Kelly told Mr Leonard that recent polling put Labour at an “unacceptably low” level of 14%, adding that the leader had “negative ratings even among our own supporters”.

I have no confidence in your ability to shape the party's message, strategy and organisation

In his resignation letter he told Mr Leonard: “Such poll ratings would produce a catastrophic result from which our party would struggle to recover.”

Mr Kelly said he had seen “no evidence” of a plan to reverse the party’s fortunes, telling the leader: “The situation has been apparent for some time and you have failed to turn things round.”

He continued: “I have no confidence in your ability to shape the party’s message, strategy and organisation.

“I know that this is a view shared by other parliamentarians, party members and indeed many members of the public.”

Meanwhile, Ms Marra said: “Richard is a stalwart of our party but he cannot lead us. That’s the unavoidable truth and change is our best hope.”

Mr Leonard was elected as Scottish Labour leader in 2017, after his predecessor, Kezia Dugdale, stepped down.

Mr Johnson, the Edinburgh Southern MSP, said he had attempted to raise concerns and make “constructive suggestions” over Labour’s future, but “these have gone unheeded and there has been no change in approach or performance”.

He added: “Continuing like this will be disastrous for our party and is why I no longer have confidence in Richard Leonard’s leadership.”

MSP Rhoda Grant gave her support to the under-fire leader, saying Mr Leonard had been elected to the post with the “overwhelming backing of members and affiliated unions”.

She added: “The crisis facing our country requires bold thinking and it requires a united Scottish Labour Party, under the leadership of Richard Leonard, fighting for the real change we need.”

A spokesman for UK Labour leader Sir Keir Starmer said: “This is a matter for Scottish Labour but Keir and Richard have a very good working relationship and they are both focused on next year’s Scottish elections where we are determined to take on the SNP and challenge them on their domestic record.”

Sir Keir last spoke to Mr Leonard last week, the spokesman added.

Mr Leonard issued a statement on Wednesday evening, saying he was “disappointed” in the timing of Mr Kelly’s resignation.

He said: “The Labour Party needs to be outward-facing not turning in on itself.

“We’ve been winning the argument and that makes it all the more disappointing that today has been the day when this has come to light.

“I’m concerned that this signals that there is too much inward-looking inside the group at Holyrood and not enough outward-facing.

“And I think that that frankly calls into question whether some of these people are the best people to stand for the Labour Party at the elections next year.”