Keir Starmer told his staff on his first day in office their duty was to return politics to service and to end self-interest.

Yet it has taken less than a month for negative, personal briefings from within Downing Street to emerge in the press, suggesting all is not entirely well in the working relationship between the two big beasts close to the prime minister: , the prime minister’s chief of staff, and , Labour’s election strategy guru.

It had been thought that after the election there would be a clear division of labour, with Gray focusing on operational delivery, while McSweeney was always expected to be top dog when it came to politics, having had the prime minister’s ear since masterminding his succession from Jeremy Corbyn.

However, after the election, gossip began to seep out of No 10, showing that a power struggle was under way. In the early days, a source claimed: “Morgan’s desk will be outside the No 10 study and he will be in and out of Keir’s office more than Sue. But look out for the fireworks.”

Just over a week later, it was reported that Gray had twice moved McSweeney’s desk further away from the prime minister’s office. It was also reported that Simon Case, the cabinet secretary, had refused to authorise Gray’s request for McSweeney to be denied access to a secure computer system unless he heard it from Starmer himself.

No 10 and Whitehall officials have vehemently rejected claims McSweeney had been blocked from getting security briefings, noting if someone really needed access they would get it.

Whitehall sources say Gray’s “centralisation” of government has left some advisers frustrated and concerned.

One Labour government source said: “There has been a massive centralisation under Sue Gray. Under the last government four people controlled what went into the PM’s box and now it’s one. Things have slowed down. She’s put herself into a position where she is extraordinarily powerful.

“There’s a suspicion that she’s making a lot of decisions on the PM’s behalf and that he wouldn’t necessarily agree with them. She’s in a position where his successes are going to be attributed to her but she’s overly vulnerable when things go wrong.”

They added that the reshuffle “taking so long was a problem” and that was down to Gray micromanaging personnel, having to sign off who was getting every job and which special advisers (spads) would be appointed.

Gray also raised eyebrows after appearing to be the only person allowed to take a Labour party staffer, her personal assistant, into the civil service, while blocking others from bringing in similar hires from the Southside HQ. However, Whitehall officials have noted such appointments are allowed as long as the position is extremely junior and for a fixed-term contract.

“Most special advisers do not want to fuck with her,” one insider said, as they had been put on strict four-month probation periods. “They’re all desperate to prove their loyalty and worth to her as she is big on experience over politics.”

Gray has also been accused of slowing down the ministerial appointments process because she wants “someone she’s hired in pretty much every department and office to be her eyes and ears”, according to another Whitehall source.

A former Labour adviser said there were signs of a “bottleneck” in government after marked delays in the appointment of Starmer’s ministerial team and then special advisers. “There has been a bit of grief about Spads – people being promised Sue would take care of them and then being left in the cold. Sue was definitely very personally involved in the Spad appointments process.”

Another government Labour source noted that while Gray was “good at what she does”, and “extremely likable”, the current position was untenable. “She’s worse than [former Boris Johnson adviser Dominic] Cummings but gets a free pass because she’s so kind and personable, while he was horrible and disliked by pretty much everyone.

“She’s been ringing up ministers offering them jobs, and ensuring she also appoints Spads so they will be reporting back to her. But these are all political relationships. This might end up becoming quite dysfunctional as she’ll have a lot of power, but since it will be around her it will cause problems. Things aren’t run like this ordinarily.”

Another added: “Her big thing is that we need experience over politics in government. But eventually, we may realise the politics is just as valuable; when it comes to the end of this year and we’ve got to argue why the prisons are still full, Thames Water is at the brink of going bust, and loads of councils are going bankrupt. We’ll need political minds in government then, not just people who have experience.”

They pointed to Patrick Vallance being scolded last month for calling for a relaxation of visa rules, which is not government policy.

Some sources claim Gray suspects McSweeney’s allies of being behind negative briefings accusing her of “micromanaging staff”. One said: “If the briefings don’t stop, Keir will end up getting rid of some people as he just hates this stuff.”

While it may seem to many that the two masterminds are at loggerheads, a No 10 source insisted Gray and McSweeney had worked together well in Downing Street and respected each other’s different but complementary strengths. They noted that Gray has decades of experience and understanding of the machinery of government, and the response to the riots showed how invaluable her experience was in supporting the PM on cross-government coordination.

A cabinet minister said the claims against Gray were “absolute bullshit”, adding: “These are just disgruntled people trying to muscle their way in. There is zero micromanagement from No 10 on the delivery of government.”

Another cabinet minister said: “Sue has a very clear commitment to cabinet government, and trusting ministers to do the job. Sue is only interested in one thing: helping the prime minister and cabinet to deliver the mandate on which the government was elected.”

A government source added: “Sue is doing a stellar job and she’s a serious player who is a force to be reckoned with. But she happens to be a woman and come from a working-class background, which is not seen at the height of government. There aren’t many people who can say they haven’t been fully supported by Sue.”