Keir Starmer will chalk up 100 days as prime minister next Saturday.

He will do so without his now-former chief of staff Sue Gray, who today carried the can for the chaos which has engulfed the government since Labour’s landslide election victory just three months ago.

Although the official line from No.10 was that Gray resigned, HuffPost UK has learned that the PM ultimately decided that she had to go.

A senior Labour source said: “Change was needed. Things weren’t working properly. Better to do it now than let it drag on.”

It is understood that the final straw was the decision, blamed on Gray, that Starmer should pay back around £6,000 for hospitality and gifts he has received from Labour supporters since becoming prime minister.

The move appeared to be an admission of guilt by the PM, and inevitably led to other ministers being asked whether they would be following suit. So far, none have done so.

“That was the nail in the coffin,” said one senior Labour figure.

Another insider added: “This is Keir’s usual pattern – something drifts on for a while and then he acts hard and ruthelessly.”

Gray has also been blamed for the new government’s complete failure to set the political weather since July 4.

As Starmer’s chief of staff in opposition, it was thought that she would use her vast experience from her time in the civil service to meticulously draw up and then implement Labour’s plan for government.

“People are annoyed about the lack of preparation,” said one Downing Street source. “It’s actually unforgivable.”

Last month’s Labour conference – which Gray did not attend – was supposed to be a reset moment.

But the row over freebies for senior Labour figures has refused to go away, completely overshadowing the government’s attempts to get back on the front foot.

Meanwhile, rumours about the bad blood among Starmer’s officials – in particular the long-running feud between Gray and the PM’s chief adviser, Morgan McSweeney – continued.

She acknowledged the damage that was doing in her resignation statement, in which she admitted that the speculation about her own position had become “a distraction to the government’s vital work”.

To add insult to injury for Gray, McSweeney has replaced her as chief of staff as part of a major shake-up inside No.10.

One government aide said: “Morgan’s the political equivalent of Yoda. He will be outstanding.

“He ran one of the most disciplined, strategic and successful election campaigns in history. People said we could never win the party back from the hard left – Morgan did it.”

Gray has not disappeared completely, and her new role as Starmer’s envoy for the nations and regions will be an important one, albeit far less influential than her previous job.

The Tories – many of whom have never forgiven Gray for her partygate report which ultimately led to Boris Johnson’s removal from office – can hardly believe their luck.

“Sue Gray was brought in to deliver a programme for government and all we’ve seen in that time is a government of self-service,” said a Conservative spokesperson. “The only question that remains is who will run the country now?”

With a parliament-defining Budget barely three weeks away, Starmer needs to quickly show that he is the one calling the shots. His decision to oust Sue Gray is his first step towards doing just that.