An exodus from Sir Keir Starmer's top team continued on Wednesday night as one of his closest aides resigned.
Chris Ward, the Labour leader's speechwriter and deputy chief of staff, told officials he was leaving after seven years at Sir Keir's side.
Only one of the "gang of five" of the leader's closest aides now remains after Labour's loss in the Hartlepool by-election in May prompted an exodus of the party's top officials.
Labour's drubbing at the polls in Hartlepool and Chesham and Amersham has provoked unease within the party about its chances at the next election.
One insider said there was a "feeling that parts of the operation hadn't worked for a while".
"These guys have been with Keir for a long, long time," the source said. "We don't have huge numbers of people with experience doing this in government, let alone in opposition."
A shadow cabinet source said Sir Keir had replaced key figures in his office with staff who had more experience of national campaigning.
"He's gone for a very experienced team and I think you will see that in the way they try to provide more definition for Keir," the source added.
A Labour source stressed that Mr Ward had left the party for "purely personal reasons" and was stepping away from politics, although he may return to work for Sir Keir in the future.
The source suggested that the easing of the pandemic and the parliamentary recess, which began last Thursday, had given officials a convenient time to leave the party.
The Telegraph understands that Mr Ward was not sacked but left his post voluntarily.