A close ally of Scottish Labour leader Richard Leonard has stood down from the party’s frontbench.
Neil Findlay, Scottish Labour’s constitutional relations spokesman, as well as business manager and party liaison, warned the party needs to stop its “self-inflicted harm” of infighting to be able to “win again”.
He also announced he will stand down as an MSP at Scottish Parliament elections in 2021.
His resignation comes a day after the party had its worst-ever result in the European elections in Scotland, losing its two MEPs and dropping from second to fifth in the polling.
In his resignation letter, Mr Findlay set out a six-point plan to “rebuild” the party, including to “end the eternal, internal fighting within our party and the toxic culture of leaks and briefings that come from some within the Scottish and UK parliamentary groups”.
He added: “This self-inflicted harm has to stop – our party leaders and our leadership teams deserve so much better.
“Scottish Labour will win again when the focus is on the public and not on the internal politics of the parliamentary group.”
Mr Findlay played a key part in the pro Jeremy Corbyn faction of Scottish Labour which took control from colleagues seen as more centrist after Mr Leonard was appointed successor to former leader Kezia Dugdale.
The Lothian MSP said he had been considering resigning for six months and made his final decision in March, intending to announce it in June but bringing it forward after the European election result.
He added: “It has been an enormous privilege to serve the Scottish Labour Party, first as a councillor and then a Member of the Scottish Parliament.
“I am proud of the work I have done representing my constituents in the Lothian region and of the campaigns I have led in Parliament most notably to retain the children’s ward at St John’s hospital, supporting the blacklisted construction workers, the mesh campaign, miners’ justice and support for the victims of undercover policing amongst many others.
“I will continue to work hard and diligently on these and other issues right up until I leave Parliament.”
In his reply, Mr Leonard thanked Mr Findlay for his “unstinting support for me as leader” and agreed the party would only advance “when we look decisively outward to the public rather than in on ourselves”.
He added: “I am very sorry that you will not be able to be a member of the Scottish Labour frontbench but I also know from our conversations that this is the right decision for you personally and in that you have my full support.
“Your service as an MSP has been outstanding. You have served the communities you represent with dedication and on the basis of your strongly-held principles.”