Keir Starmer's top Commons aide has quit amid ongoing recriminations over the grim local election results.
Carolyn Harris, who served as the Labour leader's eyes and ears in parliament, stepped down on Tuesday amid allegations she had been behind negative briefings about Angela Rayner.
In a statement, she said: “It has been the proudest moment of my career to co-chair the campaign that saw Keir Starmer elected as Labour leader, and to serve as his PPS for the past year.
“Stepping back from this role is the right thing at this moment, coming as it does after some trying personal times and an ever-increasing workload as Deputy Leader of Welsh Labour.
“I have enjoyed every minute, and look forward to supporting Keir the best way I can in the months ahead.”
A furious row broke out at the top of the party after Labour lost the Hartlepool by-election to the Tories, alongside a critical mayoral race in the West Midlands and councillors across England.
Mr Starmer's attempts to reshuffle his top team were plunged into chaos when he attempted to move Ms Rayner from her role as party chairman, which was seen as a demotion.
She was eventually handed a beefed up post of Shadow Chancellor to the Duchy of Lancaster in a reshuffle announced late on Sunday night.
Ms Harris, the MP for Swansea East and Welsh Labour's deputy leader, was reportedly accused by some MPs of negative briefing about Ms Rayner over the weekend.
“She was briefing salacious rumours about Angela over the weekend and got caught. She’s a total wrecking ball and has done him a lot of harm in [the parliamentary Labour party],” a shadow minister told The Times .