Jenny Chapman, a Labour peer, has left her job as Keir Starmer’s most senior adviser.
It comes after Labour’s defeat to the Tories in the Hartlepool by-election.
There are also fears the party is on course to lose the Batley and Spen by-election on July 1.
While she has been moved from her role at Starmer’s side, Chapman has been given a seat in the shadow cabinet and the job of going up against Brexit minister Lord Frost.
Chapman has long been a key supporter of Starmer, having served in his shadow Brexit team before running his party leadership campaign.
Having lost her Darlington seat at the 2019 election, she was handed a seat in the House of Lords.
Starmer’s communications director Ben Nunn and his deputy Paul Ovenden have also left in recent days.
And Morgan McSweeney, Starmer’s chief of staff, has been moved sideways to a new role.
