Labour leader Sir Keir Starmer has continued to overhaul his top team with his chief adviser being moved aside to a new role, it is understood.

Baroness Chapman has been ousted from her role as Sir Keir’s closest aide, the PA news agency understands, as the Opposition leader looks to avoid another disastrous by-election defeat.

Labour lost Hartlepool to Boris Johnson’s Conservatives in May and polling suggests the party could be about to see defeat in another seat in its traditional heartlands when voters go to the polls in Batley and Spen next month.

Reports have suggested former Darlington MP Baroness Chapman, who chaired Sir Keir’s campaign to succeed Jeremy Corbyn as party leader last year, will be shifted from her aide role and given a job in the shadow cabinet to act as Brexit minister Lord Frost’s opposite number.

There have been whispers of a fallout between some Labour MPs and Baroness Chapman – who is said to be a member of Sir Keir’s inner circle, having previously served in his shadow Brexit team before he became leader – with some in the Parliamentary Labour Party blaming her for the party’s poor showing in May’s local elections.

The move is a further overhaul of Sir Keir’s top team after a number of changes were announced over the weekend.

Chief of staff Morgan McSweeney is set to move to a “strategic role” with less of a focus on day-to-day activities, a Labour source said, after the party’s dismal result in the Chesham and Amersham by-election.

Deputy communications chief Paul Ovenden is also stepping down, but for family reasons.

Following the loss of the former stronghold seat of Hartlepool, concerns have grown over Labour’s prospects in the July 1 by-election in Batley and Spen, which was Jo Cox’s seat.

A new poll put the murdered MP’s sister, Kim Leadbeater, on course to lose the heartlands constituency in Yorkshire to the Conservatives.

The Tories were on 47% – up 11% from the 2019 general election – while Labour was on 43%, according to Survation’s phone poll of adults earlier this month.

Scrutiny of Sir Keir’s leadership will intensify if he loses Batley and Spen, having overseen the crushing defeat to the Tories in the former heartland town of Hartlepool last month.

The Batley and Spen by-election was triggered after Tracy Brabin, who won the seat for Labour in 2019 with a 3,525 majority over the Conservatives, was elected as the mayor of West Yorkshire in May.

Labour secured just 622 votes in the by-election, taking just 1.6% of the vote and losing its deposit in the process.

Polling expert Sir John Curtice said it was the “worst Labour performance in any by-election”.

Communications director Ben Nunn announced he was standing down from the role following that performance, but told colleagues he remained convinced Sir Keir “will be a great prime minister”.