Fears have been raised that Sir Keir Starmer‘s controversial chief of staff could seize even more power when the UK’s top civil servant is replaced.

Sources warn that Sue Gray, who yesterday was accused of denying the Prime Minister vital security briefings by blocking access to him, would dominate one of the leading contenders to be the next Cabinet Secretary.

Senior politicians have also expressed alarm that she is already embroiled in a toxic power struggle inside No 10 just a month after the election.

As the Mail told on Saturday, Ms Gray is facing allegations that she is ‘dominating negotiations’ over the controversial £310 million redevelopment of Casement Park stadium in Belfast. And The Mail on Sunday revealed claims that Ms Gray, who led the Partygate investigation, ‘thinks she runs the country’.

Ms Gray (pictured) is facing allegations that she is ‘dominating negotiations’ over the controversial £310 million redevelopment of Casement Park stadium

Pictured, Sir Oliver Robbins, a former civil servant who negotiated Theresa May’s disastrous Brexit deal

Even current Cabinet Secretary Simon Case is said to have been forced to ask her permission to speak to Sir Keir.

There are now concerns that the situation could deteriorate still further next year if, as expected, Mr Case steps down.

Among those being lined up to replace him is Sir Oliver Robbins, a former civil servant who negotiated Theresa May’s disastrous Brexit deal. One senior Whitehall source told the Mail that Robbins would be Ms Gray’s ‘patsy’.

A senior Tory added: ‘What we are seeing is Sue Gray wants complete and utter control and Starmer seems to be comfortable with that, he seems to think she is vital.

‘The result will be she decides who goes where including the Cabinet Secretary. Sue Gray would love the idea of Olly Robbins being there, he is completely and utterly her man.’

Even current Cabinet Secretary Simon Case (pictured) is said to have been forced to ask her permission to speak to Sir Keir

But former Cabinet minister and Mail columnist Nadine Dorries predicted that instead Ms Gray will have to be moved out of Downing Street.

She added: ‘Sue Gray has already upset so many people and created so many ructions inside No 10 and in the Cabinet, it’s only a matter of time before Starmer has to move her on to quell the ever-rising unhappiness from his aides and ministers.

‘There is no way the PM’s office can continue to run like this. She’s Dominic Cummings mark 2 and it will all end in tears.’

Former Cabinet minister Sir Iain Duncan Smith said: ‘It bodes ill when the senior civil servant becomes the story because of other people’s deep distrust of her.

‘This is only week six and there are already splits and divisions.’

A Downing Street source insisted: ‘The only power is with ministers not staff.’