Mr McDonald, who was shadow employment secretary until Monday, quit during Sir Keir Starmer’s first in-person party conference as leader, claiming he was told by the leader’s office to argue against a £15 per hour minimum wage and bringing statutory sick pay up to the same level as the living wage.
The current Labour Party policy – as part of a “new deal for workers” – argues for an immediate minimum wage increase under a Labour government to £10 per hour and was launched earlier in the conference.
In a letter to Sir Keir, the former frontbencher said making the argument was “something I could not do”.
Speaking on BBC Scotland’s Good Morning Scotland programme, shadow Scottish secretary Ian Murray said: “We’re not quite sure why he resigned yesterday, he seems to have said one thing and written another.
“That looks as if it might be a planned sabotage of conference, rather than it being about any principle.”
He added: “This was a policy, don’t forget, that Andy McDonald and the shadow cabinet wrote, he put through shadow cabinet and he launched with much acclaim in the conference hall 48 hours before he resigned.
It's not the kind of language we should be using in politics
“We’re not quite sure why he resigned, but these things happen in politics and we’re all very angry and frustrated that the headlines are being dominated by one person when we should be talking about the big issues of the future.”
The comments from Mr Murray are likely to exacerbate an already widening gap between the centre ground and left wing of the party.
Just hours after Mr McDonald’s resignation, MP Zarah Sultana told a rally it was “shameful” he had been asked to argue against the wage hike, hitting out at the “Blairite clique running the show”.
Rebecca Long-Bailey – one of the party’s leading MPs on the left and one of Sir Keir’s rivals in last year’s leadership race – told the same conference fringe event: “If it’s true that we were saying that we shouldn’t advocate for statutory sick pay at the rate of the living wage, then what is the point of the Labour Party?”
Andy McDonald quits shadow cabibet pic.twitter.com/6vcEORphGG
— Sam Coates Sky (@SamCoatesSky) September 27, 2021
Mr McDonald went on to attack the leadership of Sir Keir, saying: “I joined your frontbench team on the basis of the pledges that you made in the leadership campaign to bring about unity within the party and maintain our commitment to socialist policies.
“After 18 months of your leadership, our movement is more divided than ever and the pledges that you made to the membership are not being honoured. This is just the latest of many.”
Mr Murray again called for an apology from his party’s deputy leader, Angela Rayner after she called the Tories “scum”.
“I said quite clearly yesterday she should apologise for that,” he said.
“It’s not the kind of language we should be using in politics.
“We need to be professional and respectful of each other – we can have robust debates without resulting in using language like that and we have to as politicians and public figures set an example for people.”