Morgan McSweeney, a man instrumental to the rise of Sir Keir Starmer, is at the centre of another political row after wave of anonymous briefings exposed tensions at the heart of government.

Senior ministers have called for Sir Keir Starmer to impose order on the Downing Street operation run by Mr McSweeney, his chief of staff, after media outlets were given reports cabinet colleagues were plotting leadership challenges.

Some in government have blamed the 48-year-old adviser for being behind the briefings – and of importing a culture of off-the-record chats with journalists from opposition into Downing Street.

He has not commented on the criticism – like most people in behind-the-scenes roles in government he is not allowed to appear before the TV cameras to defend himself.

And he has always sought to keep a low profile in any case. Until recently, there were few pictures of him in circulation.

He derives his power and influence from his track record as a political strategist – he masterminded Labour’s landslide 2024 general election victory and Sir Keir’s 2020 Labour leadership bid.

Like previous powerful, but unelected, advisers in Downing Street, such as Dominic Cummings or Alastair Campbell, he has been the target of negative stories.

His closeness to Sir Keir – as a seasoned political operator to a relatively inexperienced prime minister – means he can be seen as “proxy” for the PM.

One ally of the prime minister told the BBC: “They are coming for Morgan because they want to get Keir.

“This isn’t a parliamentary party battle, it’s a Labour elite battle.”

Mr McSweeney emerged victorious from an internal power struggle to become Sir Kier’s chief of staff last year after the dramatic resignation of Sue Gray.

Born in Macroom, County Cork, Mr McSweeney joined Labour under Tony Blair, working in a junior role at the party’s headquarters.

He later started working for Steve Reed, who is now environment secretary but at the time was a councillor in Lambeth, south London, where he was trying to regain control of the party from the hard left.

In 2006 Mr McSweeney helped run the party’s successful campaign to take control of the council, with Reed becoming leader.

His reputation as a skilled campaign strategist was further cemented in Barking and Dagenham, where the far-right, anti-immigrant British National Party was gaining support and hoping to win its first parliamentary seat 2010.

Mr McSweeney played a key role in the fight to defeat the BNP in the area, with a campaign which focused on local issues.

However, his campaigns were not always a success – in 2015 he ran Blairite Liz Kendall’s bid to become Labour leader, where she secured only 4.5% of votes in the contest won by Jeremy Corbyn.

In 2017, Mr McSweeney became a director of the think tank Labour Together, which opposed the direction of the party under Corbyn and went on to back Sir Keir.

The Electoral Commission later fined Labour Together £14,250 for late and inaccurate reporting of donations during the period when Mr McSweeney was a director.

The fine later fuelled calls from Conservative MPs for a deeper investigation into Labour’s campaign finances – though the Electoral Commission decided not to reopen an investigation.

At the time of the fine, McSweeney had left Labour Together to run Sir Keir’s 2020 leadership bid, later becoming his chief of staff in opposition, where he played a key role in removing Corbyn supporters from positions of power.

As Labour’s campaign director, Mr McSweeney was tasked with devising the party’s strategy for last July’s general election.

Among the new Labour MPs to be elected was his wife, Imogen Walker, a former councillor in Lambeth who now represents Hamilton and Clyde Valley.

Quiet, unassuming, even shy, particularly in public, McSweeney is known for being obsessed by winning, constantly fearful of complacency and ever aware of Labour’s track record of losing far more often than it wins.