Ms Gray, the Prime Minister’s chief of staff, and Morgan McSweeney, his most senior aide, are understood to be at loggerheads.

Reports emerged over the weekend claiming that Ms Gray, the former civil servant, who investigated partygate, was being accused of preventing Sir Keir from receiving security updates by blocking access to him.

It is understood that Mr McSweeney disputes all the claims made about him, and Number 10 insiders have dismissed the idea that the Prime Minister could be blocked from receiving important security information.

Ms Gray, the most senior political official in Number 10, is said to have tried to block Mr McSweeney from having access to a secure government IT system.

Simon Case, the Cabinet secretary, reportedly got upset with her demand and told her, "I will only authorise that if the Prime Minister tells me himself." The Mail was also informed on Sunday by a security source that Ms. Gray had attempted to prevent them from giving Sir Keir a straight briefing on a crucial issue pertaining to national security."We have stated that the PM needs to receive an intelligence briefing, and Gray has responded, 'tell me,'" the insider stated. However, we must be aware that he has received it. Major security problems are considered in weekly National Security Council meetings, which Sir Keir leads, according to a Downing Street source. He also meets "regularly" to discuss security issues.The reports will fuel speculation of a power struggle between the pair, which could force Sir Keir to decide whether to dispense with one of them. 

He is known to have a low tolerance for the sort of factional infighting that has beset previous administrations, including Boris Johnson’s.

Mr McSweeney is Number 10’s head of political strategy, and has been Sir Keir’s senior adviser since he became Labour leader in April 2020.

Ms Gray was poached by Sir Keir in March last year to become his chief of staff and make his operation ready for government.

There has been disquiet within Labour’s ranks over her powerful role, which included her reportedly exerting heavy influence over the appointment of ministers.

Jess Phillips, the safeguarding minister at the Home Office, has revealed that it was Ms Gray who rang her up to offer her the job.