Lord Geidt's resignation as Boris Johnson’s ethics chief has dealt a fresh blow to the PM's beleaguered premiership as the fallout from the Partygate scandal continues.
He became the second ministerial interests adviser to resign during Mr Johnson's three years in office, when a brief statement was published on the government website announcing his departure.
The crossbench peer's dramatic exit made headlines on Wednesday, but his name remains largely unknown to the public, despite holding huge sway in politics.
So, who exactly is the man whose resignation threatens to derail the prime minister's grip on office and what did he do while he was Mr Johnson's ethics chief?
What issues did Lord Geidt have to deal with while he was the PM's ethics adviser?
Lord Geidt's predecessor Sir Alex Allan quit in 2020 after Mr Johnson refused to accept his finding that Home Secretary Priti Patel had bullied civil servants.He began the job last April by leading an inquiry into the funding of renovations to Mr Johnson’s Downing Street flat following reports over the cost of the work.
His report, which was published the following month, found Mr Johnson had not broken the ministerial code over the refurbishment.
Lord Geidt later launched a probe into former health secretary Matt Hancock after it was reported he held shares in a family company which had won an NHS contract.
In May 2021, the ethics adviser concluded that Mr Hancock had committed a “minor” but undeliberate breach of the ministerial code and should not resign from his post.
In April this year, Lord Geidt also cleared Chancellor Rishi Sunak of breaching the ministerial code over the tax affairs of his family.
Mr Sunak’s wife, Akshata Murty, was reported as holding non-domiciled tax status, exempting her from paying UK tax on overseas earnings.
Lord Geidt found two instances where Ms Murty’s tax status “could have given rise to a conflict of interest” for the Chancellor.
But he found in the first instance the issue was properly declared, and in the second Mr Sunak assured a Treasury change for some non-dom individuals did not affect his wife.
Why did Lord Geidt suggest the PM may have broken the ministerial code over the Partygate scandal?
Last month, Lord Geidt suggested Mr Johnson may have breached the ministerial code after being fined following partygate.
Mr Johnson responded that the fixed penalty notice he was given by the Metropolitan Police “did not breach” the ministerial code as there was “no intent to break the law”.
On Tuesday, Lord Geidt reiterated his comments during an appearance at the Commons Public Administration and Constitutional Affairs Committee.
The committee noted that he had been given a “small pool” of staff to help him following a request he made to Mr Johnson in December, a move which he said had been “very helpful”.
Two weeks ago, ITV News Political Correspondent Carl Dinnen analysed how much extra trouble Lord Geidt's intervention spelt for the PM
He added: “I’m very glad to have it because the amount of traffic that comes to the Office of Independent Adviser has grown very greatly in my time.”
Questioned why, he told MPs: “I think matters relating to the code have become a matters of greater profile in the public square.”
Lord Geidt also told MPs on the committee he had felt “frustration” over partygate and that the option of him resigning was “always on the agenda as an available remedy to a particular problem.”
According to The Guardian, one person who had spoken to him said he was “sick of being lied to".
Another person was said to have believed he was “frustrated” at his portrayal as a “patsy”, the paper reported, with him then finally sending a strongly worded letter to the PM on Wednesday after a "long night of the soul".
What has been the immediate political reaction to Lord Geidt's dramatic resignation?
A government spokesperson said officials were surprised by his exit, given his "commitment to the role".
"We are surprised by this decision, given Lord Geidt’s commitment to the role, to the Prime Minister, and in his evidence to the House of Commons just yesterday," the statement said.
"This week, the independent adviser was asked to provide advice on a commercially sensitive matter in the national interest, which has previously had cross-party support. No decision had been taken pending that advice.
"Whilst we are disappointed, we thank Lord Geidt for his public service. We will appoint a new adviser in due course."
The PM is said to be totally surprised by the resignation. A senior source told ITV News Political Correspondent Daniel Hewitt that the sudden departure remains a "mystery" to Mr Johnson, as on Monday he allegedly asked if he could stay on for another half of a year.
Labour former minister Chris Bryant tweeted that "Christopher Geidt is one of the most honourable men I have ever met". “In the end he was a decent man working for an indecent prime minister," he wrote. “He thought he could discreetly bring about incremental change but he was repeatedly lied to by No 10. In honour Johnson should resign."
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To know
What was Lord Geidt's career before he entered politics?
He began his career in the royal household as an assistant private secretary in 2002.
Three years later he was appointed deputy private secretary to the Queen before moving to the top job.
He had previously worked for the Foreign Office, as well as the UN in Sarajevo, Geneva and Brussels and is a graduate of King’s College, London.
Lord Geidt spent a decade acting as a channel of communication between Downing Street and the monarch until 2017.
He was knighted under the Royal Victorian Order, for service to the monarchy, and was later made a knight commander of the Order of the Bath, for public service.
The crossbench peer entered the Lords after stepping down from his role with the royal household, becoming Baron Geidt of Crobeg.