Boris Johnson has set aside plans for a radical overhaul of Whitehall machinery in favour of a modest shakeup of his top team on Thursday, in the latest indication that his approach to government may be less revolutionary than that of his key adviser, Dominic Cummings.

After giving the go-ahead to the controversial HS2 rail project, which Cummings was known to be sceptical about, Johnson appears to have rejected – or postponed – proposals to merge or abolish government departments. Instead, several cabinet ministers who are deemed by Downing Street to have performed poorly in recent months are likely to be shown the door.

Those whose jobs are widely believed at Westminster to be under threat include the business secretary, Andrea Leadsom, the environment secretary, Theresa Villiers, and the attorney general, Geoffrey Cox.

But Sajid Javid, who has clashed with Cummings, appears safe, with Rishi Sunak also left in place as chief secretary of the Treasury.

There had been fears that the shakeup would tip the gender balance around the cabinet table in favour of men – but No 10 sources insist the total number of women attending cabinet will not decline. They also claim the prime minister will promote talented backbenchers to more junior posts, creating a pool of candidates with enough experience to enter the cabinet in future.

“The prime minister wants this reshuffle to set the foundations for government now and in the future,” a No 10 source said. “He wants to promote a generation of talent that will be promoted further in the coming years. He will reward those MPs who have worked hard to deliver on this government’s priorities to level up the whole country and deliver the change people voted for last year.”

The new intake of MPs, many of them women, are likely to be brought into the most junior government posts in the coming days to cement the impression that Johnson is committed to gender equality.

Cummings has written extensively in the past about the need to overhaul the machinery of government, and there had been speculation about drastic changes, including an economics and business super-ministry to mastermind Johnson’s “levelling up” plans.

These ideas appear to be off the table for the moment. Some senior Conservatives suggest Johnson may not have the appetite for the necessary upheaval. “He doesn’t like conflict at all,” said one government source.

But others said the spending review, expected in summer or autumn, would be a more natural point to reshape Whitehall. When Cummings was asked about the reshuffle on Tuesday, he said, “PJ Masks will do a greater job than all of them put together” – a reference to a children’s TV show.

Johnson will summon sacked ministers to his House of Commons office in the morning to deliver the bad news before returning to Downing Street to welcome the parade of those who are being promoted. Plum jobs due to be filled include culture secretary, a job which Nicky Morgan made clear she would only do for a few months when Johnson handed her a peerage after the general election.

Johnson is also expected to announce who will be the new HS2 minister – a new post created to ensure that Downing Street can exert a firm grip on the delivery of the mega-project – and who will oversee the COP26 climate conference.

Cox, who put his booming baritone to good use introducing Johnson at his leadership campaign launch, did little to dampen speculation that he would be removed from office on Wednesday. Asked at an Institute for Government event if he would be disappointed to leave his job, he said: “It has been an enormous privilege to do this job. But it is a decision for the prime minister.”

Cox has been tipped to chair the government’s review into the role of the judiciary, including the supreme court, and he suggested he would be willing to take on that role. He said the new constitutional commission would consider both the role of judicial review – which he described as the “judicialisation of politics” – and the appointment of judges to the supreme court.

The Department for International Development appears to have escaped immediate annexation by Dominic Raab’s Foreign Office, a move charities have warned strongly against. But with the prime minister’s foreign policy adviser, the academic John Bew, understood to be conducting a review into Britain’s post-Brexit role in the world, that change could yet come later this year.

The international development secretary, Alok Sharma, is expected to be promoted, while Brandon Lewis could be for the chop from his Home Office post. Party sources suggest Lewis’s decision in 2018 to investigate Boris Johnson’s comments on women in Islamic dress looking like “letterboxes” is a mark against him.

They claim he was only appointed to the senior Home Office role in July last year because he had previously served as Tory party chairman. To get rid of him at that point would have looked “too brutal” as one of the first acts of the new prime minister, the source said.

Johnson was cleared of any wrongdoing over his controversial Telegraph column and Tory MPs rallied around him, demanding an apology from Lewis for launching the investigation. The row has not been forgotten, the source suggested. Victoria Atkins is expected to take on the brief.