Case, who has served four prime ministers and 120 cabinet ministers in the role, said he would stay in post while the process to replace him got under way.
His long-planned departure on health grounds comes after a turbulent few weeks for the Downing Street operation marked by damaging leaks and internal rows, with Keir Starmer understood to have grown increasingly frustrated.
Cabinet ministers and senior aides have urged the prime minister to "get a grip" on the situation to avoid it undermining the government.
The departure of the UK's most senior civil servant, who is said to have had a tense relationship with Starmer's chief of staff, Sue Gray, gives the prime minister the opportunity for a reset.
Starmer thanked Case for his "support" and "years of service to our country" after the announcement, saying: "We are losing a public servant of the highest calibre.
"It is right that Simon takes time now to focus on his health, and he should know that he does so with the well wishes of this government and all those who he
The energy price cap, set by the industry regulator, Ofgem, and covering October to December, will rise by 10% to £1,717 a year for an average dual-fuel household in Great Britain paying by direct debit.
Denne historien er fra October 01, 2024-utgaven av The Guardian.
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Denne historien er fra October 01, 2024-utgaven av The Guardian.
Start din 7-dagers gratis prøveperiode på Magzter GOLD for å få tilgang til tusenvis av utvalgte premiumhistorier og 9000+ magasiner og aviser.
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Debt, IT woes and no chief executive What returning Asda boss has in store
Allan Leighton faces a back-to-thefuture challenge as he once again takes charge at struggling Asda.
Sweeney's RFU salary rises to £1.1m amid job cuts and losses
The Rugby Football Union chief executive, Bill Sweeney, was paid £1.1m for the 2023-24 financial year despite record losses and swingeing job cuts at the governing body.
'Probably more out than in' Salah leans towards exit with Liverpool yet to offer new deal
Mohamed Salah says he is disappointed Liverpool have not offered him a new contract and feels \"probably more out than in\" in terms of staying beyond the end of the season.
Reds' contract dance with Salah was always likely to be complex
Revamp after Jürgen Klopp's exit did not help and time is short for Liverpool to make their talisman feel wanted
Guardiola insists ageing squad is not behind City's alarming drop in form
Pep Guardiola has denied that a key factor in Manchester City's run of five consecutive defeats is that nine of his squad are aged 30 or older, with the manager pointing to how the same players were Premier League champions last season.
Wan-Bissaka seals West Ham win to take heat off Lopetegui
On a bitterly cold Tyneside night, West Ham finally remembered how to fight back.
Arteta seeks ruthless edge to fix away-day woes in Europe
Mikel Arteta has challenged his Arsenal team to fix their patchy European away form against a vibrant Sporting tonight, admitting they need to improve a record of one win in their past eight continental trips.
I've got my mojo back ... I actually felt unwell at the end at Chelsea'
After recharging her batteries in the US, Emma Hayes reflects on the grind of club coaching and fresh ambitions
Spurs blow as Vicario faces long spell out after surgery
Guglielmo Vicario has had surgery to repair an ankle fracture sustained in Tottenham's 4-0 Premier League win at Manchester City on Saturday.
Verstappen in 'that club' with Senna and Hamilton
Red Bull chief Horner claims his driver's fourth, and most challenging, world title puts him in same class as the greats
