LONDON — Keir Starmer has lost his closest aide. At the most perilous moment for his premiership yet, the British prime minister needs to find a replacement fast.

The chief of staff position became vacant Sunday after Morgan McSweeney — a key aide to Starmer throughout his time as Labour Party leader — resigned Sunday following revelations about Peter Mandelson in the Jeffrey Epstein files. McSweeney said he took “full responsibility” for personally advising Starmer to appoint the former Labour peer as U.K. ambassador to Washington.

It leaves a huge hole in Starmer’s struggling Downing Street operation.

The Irishman is credited with ruthlessly moving the ruling Labour Party back to the center ground of U.K. politics, and masterminding Starmer’s 2024 general election landslide.

A Downing Street chief of staff would take up post with Labour lagging behind Reform UK in opinion polls, and with Labour MPs furious about the Mandelson scandal.

Here are the contenders for the top Downing Street job being talked up in Whitehall.

Louise Casey

If a cabinet secretary vacancy doesn’t open up sooner, then the famed “Whitehall troubleshooter” that both Tory and Labour administrations have enlisted to fix some of their knottiest problems is being talked up as a frontrunner.

“She’s basically in charge of everything already,” said one official — pointing out how Starmer’s turned to her to investigate both grooming gangs and social care.

Vidhya Alakeson

Alakeson, previously a McSweeney deputy, was swiftly promoted to co-chief of staff on an “acting” basis Sunday night.

She comes from think tank land, where she had a top job at the cost-of-living-focused Resolution Foundation, and has won praise for leading Labour’s outreach to business. The policy expert gets plenty of praise from colleagues, but others fear she may be “indecisive.”

Jill Cuthbertson

Cuthbertson — the other half of the acting-up deputy chief of staff duo — is seen as having a deeper understanding of the political front, having worked with former Labour leaders Gordon Brown and Ed Miliband.

Cuthbertson is due some extended leave in the coming months, but one option under discussion is the job-share being made permanent. 

Amy Richards

A former long-time adviser to Foreign Secretary Yvette Cooper, the PM brought Richards into No.10 to bolster his operation’s communications with backbenchers.

The political director is spoken of highly among special advisers who don’t seem to lay any blame with her for the Parliamentary Labour Party’s current mood. 

Long shots ….

Outside chancers being mentioned are the PM’s chief secretary Darren Jones, comms boss Tim Allan, Starmer biographer Tom Baldwin, National Security Adviser Jonathan Powell (once Tony Blair’s chief of staff, although himself facing questions over the Mandelson appointment) and top Rachel Reeves’ adviser Ben Nunn.

POLITICO London Playbook is throwing another name out there for kicks: ex-chief of staff Sue Gray, who resigned in October 2024 after losing a power battle with McSweeney … because who doesn’t love a comeback?