Sir Keir Starmer declared his Labour government was moving into its “second phase” as the Prime Minister shook up his team in 10 Downing Street.
The Prime Minister’s top team “reset” began as one of his communication chiefs announced he was quitting after just a year in the role.
James Lyons, the son-in-law of Labour grandee Dame Margaret Hodge, is the fourth senior staff member to be replaced in the PM’s office in 12 months.
He said in a statement: “It was an honour to be asked to come in. I’m proud to have helped to get a grip on Whitehall comms after what was a difficult few first months for the Government.
“It wasn’t just filling the grid. Launching the Plan for Change brought focus and direction. But I gave up a lot to come in and this was never intended as a long haul.
“When I came back from the summer break I told colleagues I was looking to leave by the end of the year. I’ve brought this forward to be part of the other changes.”
Tim Allan, a former adviser to Sir Tony Blair's government, has been appointed the Government's executive director of communications, as the PM aims to improve communications across his administration.
It comes as Number 10 announced Sir Keir was “bolstering” Government operations and had appointed MP Darren Jones as the Chief Secretary to the Prime Minister and Downing Street.
The new role will work “collaboratively across UK Government to drive forward progress in key policy areas”, No 10 said in a statement.
Mr Jones had previously been chief secretary to the Treasury and will "directly oversee work across Government to support the delivery of the Prime Minister's priorities", Downing Street said.
Treasury minister James Murray will replace him as Treasury chief secretary while Chipping Barnet MP Dan Tomlinson has replaced him as Treasury exchequer secretary.
The appointment follows Sir Keir's recruitment of Baroness Minouche Shafik, an economist and former president of Columbia University in New York, as his chief economic adviser.
Lady Shafik's recruitment is part of a move to build economic expertise within the Government ahead of the budget this autumn, when Ms Reeves is expected to have to make tough tax and spending decisions.
The new adviser has also been deputy governor of the Bank of England and permanent secretary at the Department for International Development, a now-scrapped Government department.
The Prime Minister’s principal private secretary (PPS), Nin Pandit, is being let go after just 10 months running Sir Keir’s team in Number 10, it was reported last week.
The senior civil servant is expected to move to another role in government after the PM became concerned she was ineffective in her role, according to the BBC.
Sue Gray left as the PM’s former chief of staff in October and director of communications Matthew Doyle stood down in March.
The Prime Minister said Monday's reshuffle in Number 10 should be seen as the Government moving into its "second phase".
In an interview with the BBC's Matt Chorley, Sir Keir said: "When I took over as leader of the Labour Party, I said there will be sort of three phases to this.
"You've got to sort of build the fundamentals first and then you move on to the second stage. So, this should be seen more as moving on to the second phase than a reshuffle.”
He added that he was not "angry" about the pace of change his Government had managed, but said he was "frustrated, I get the frustration and anger of voters because they want change".
Sir Keir added: "I want to deliver that change as quickly as possible. Today is about moving on to that second phase.
"I say delivery is the absolute key word and that's why I'm really pleased with the changes today."
However Kevin Hollinrake, Conservative Party chairman, described the reshuffle as “chaotic” and said it shows a Downing Street “in crisis”.
“Totally distracted from fixing the damage they’ve done to the economy, jobs and small businesses,” he added.
“It’s like firefighters arguing about the hose whilst the house burns down.
“Inflation has doubled, borrowing costs have soared, and Britain is on the brink of a debt crisis, with working people left to pay the price through higher taxes.
“Only the Conservatives, under new leadership, will take a responsible approach to the public finances and ensure our economy grows whilst we live within our means.”
