The rift between Boris Johnson’s team and Sajid Javid is widening, government sources have said, with growing concerns in Whitehall that disagreements are harming the effectiveness of the Downing Street operation.

Two government sources said there was frustration in No 10 and other departments that the chancellor was trying to water down big spending announcements Boris Johnson wants to make at the Conservative party conference.

They said No 10 was becoming increasingly annoyed by what it regarded as Javid’s intransigence, and was sidelining him in favour of Rishi Sunak, the chief secretary to the Treasury, with departments being directed to talk to him rather than the chancellor.

Insiders said Javid was still without a chief media adviser after Sonia Khan was sacked by Johnson’s chief of staff, Dominic Cummings, and marched out of the building for maintaining contact with an associate of the previous chancellor Philip Hammond.

A Whitehall source said: “There is no sign of change, in fact it has got worse. Saj [Javid] remains furious because he is not part of the decision-making process on government expenditure. It all comes from Cummings and a small number of No 10 people. A lot of people are saying that Saj’s days are numbered. No 10 is much happier with Rishi.”

A second government source said: “Relations between the PM and the chancellor are just about OK on a personal level but there is a lot of tension at the level below that.”

He added: “Sajid is acting like he got 45% of the vote in the leadership election. He doesn’t seem to understand there’s an election coming and keeps saying he will consider policies in 2020 when this government might not even be in power then.”

It is understood No 10 is planning to make big, headline-grabbing announcements to appeal to voters on the domestic agenda, aside from Brexit, at party conference.

However, the source said Javid was being “difficult” over signing off conference policies that No 10 and departments want to implement on housing, including a more interventionist move to build more homes, and plans for a longer funding settlement for the NHS and social care.

Relations are believed to have worsened since Javid was infuriated by the sacking of Khan. It emerged that the chancellor had not been warned in advance that she was about to get her marching orders.

Khan was accused of leaking information about government strategy to Hammond, who is co-ordinating parliamentary moves to prevent a no-deal Brexit.

Khan was the fourth young woman in a month to be axed from the prime minister’s network of advisers and senior staffers, leaving Javid without a media adviser before the spending review, where he laid out details of a £14bn allocation for schools and new police funding.

She was confronted by Cummings who demanded to see both her mobile telephones, sources said. After she admitted speaking to a former adviser to Hammond, she was marched off the premises by an armed police officer.

The episode underlined simmering tensions over the summer between Downing Street and the Treasury. Javid was ordered by No 10 to scrap a planned speech on the economy, while Downing Street took the lead in announcing spending plans for health, police and prisons.

The day after Khan’s sacking, Javid took to the airwaves and refused to discuss the sacking but insisted he had a “fantastic” relationship with the prime minister.

He told the Today programme: “I’m not going to discuss any personnel issues, it wouldn’t be appropriate.

“The relationship is fantastic with the prime minister. Before he was prime minister, he is someone I got on with incredibly well. It’s a real privilege to work with him, to work closely so well on people’s priorities.”

It is understood that ministers bid for £55bn worth of spending commitments, which were cut down to £13.4bn by the chancellor.

A No 10 source said: “The PM and chancellor’s teams are working hand in glove to deliver an ambitious policy agenda. This process might ruffle a few feathers in departments, but officials in both No 10 and 11 are used to it.”