Darren Jones, the chief secretary to the Treasury, has been moved to a new senior role in Downing Street as Keir Starmer attempts to get a grip on delivery before what is likely to be a tumultuous autumn for the government.

The senior MP, whose new title will be chief secretary to the prime minster, has been put in charge of day-to-day delivery of the prime minister’s priorities after No 10 spent the summer struggling to get on the front foot on issues including the economy and migration, and lags behind Reform UK in the polls.

He will be replaced as Rachel Reeves’s deputy by James Murray, who has been promoted from exchequer secretary, a more junior ministerial role at the Treasury. In turn, his role will be taken by Dan Tomlinson, the government’s “growth mission champion”, as Starmer seeks to reward the new 2024 intake.

However, there was not expected to be a wider reshuffle of the junior ministerial ranks at this point despite some reports, senior sources said, although Starmer would need to appoint a new homelessness minister after Rushanara Ali stood down this summer. The cabinet is to stay intact.

Speaking to the BBC on Monday, Starmer rejected the idea it was a reshuffle prompted by crisis, arguing it was more a case of a new phase of government. “This should be seen more as moving on to the second phase than a reshuffle, because some of the positions are actually new positions,” he told Radio 5 Live.

Downing Street is also expected to confirm that the former Bank of England deputy governor Minouche Shafik will become Starmer’s chief economic adviser, as the government seeks to strengthen its efforts to bolster UK growth and productivity.

The communications operation will also be shaken up with Tim Allan, an adviser to Tony Blair in No 10 who went on to fund the PR firm Portland, coming in as executive director of government communications. The political role is separate from that of David Dinsmore, who has been tasked with improving the civil service communications operation.

James Lyons, Downing Street’s director of communications for strategy, is stepping down. Steph Driver, his counterpart for day-to-day No 10 communications, who is close to Starmer, stays in post, answering to Allan.

The Downing Street policy unit is also undergoing changes, after some internal conflict over who was running the department. Liz Lloyd, who was Tony Blair’s deputy chief of staff at No 10, is leaving but is expected to move to a new role in government.

Stuart Ingham, another policy chief and Starmer’s most longstanding aide, will leave the unit to work in chief of staff Morgan McSweeney’s team, taking on a more political role, which sources said would ensure the prime minister’s priorities were taken into account in every decision.

A new political policy chief is expected to be appointed shortly, but in the meantime Vidhya Alakeson, one of McSweeney’s deputies, will oversee day-to-day policy work. Sources suggested that Louise Casey, a senior government fixer, would not be coming into No 10 despite reports.

The extent of the shake-up reflects the sense that Starmer’s No 10 has increasingly struggled to impose its own narrative, and is instead mainly being shaken by external crises, notably the focus over the summer on migration, and Reform UK’s planned response to it.

Things are not likely to improve in the short term, with the return of parliament presenting Starmer and his team with a series of tough challenges, including the likely need for tax rises in this autumn’s budget and ongoing legal battles over asylum hotels.

In his BBC interview, Starmer said while he understood people’s concerns about migration, Reform and Nigel Farage were exploiting the issue as “the politics of grievance”.

“They feed on grievance. They don’t want the problem solved because they’ve got no reason to exist if the problems are solved,” he said.

Asked about a recent spate of English flags being draped on lamp-posts or spray-painted on roundabouts, Starmer said he was proud of the flag, and had one in his Downing Street flat, but was wary of it being used for “divisive” reasons.

“In our flat, which is upstairs from here, as you know, we’ve got a St George’s flag,” he said. “I think they’re patriotic, and I think they’re a great symbol of our nation. I don’t think they should be devalued and belittled. And I think sometimes when they’re used purely for divisive purposes, it actually devalues the flag. I don’t want to see that.”

Downing Street sources characterised the changes as the next step in the government’s rewiring of Whitehall, with No 10 evolving into a “command and control” operation. They acknowledged that Jones’s appointment and the new structures were about increasing government grip and focus.

Jones’s appointment is likely to be seen as an acknowledgment by the prime minister that he needs to take a bolder approach to delivering on his promises, with the Bristol North West MP seen as a Blairite-style reformer who has privately urged the government to be more radical.