The departure of Lord Geidt as Boris Johnson’s ethics tsar felt like a long time coming.

A highly-respected crossbencher, who previously served as the Queen’s Private Secretary, Geidt was appointed as Independent Adviser on Ministers’ Interests in April 2020 because of his “distinguished record of impartial public service”.

He took on the ethics adviser role in spring 2021, during one of the most turbulent periods of modern political history, with a series of responsibilities, including scrutinising all declarations from ministers.

It was clear from the moment Geidt accepted Johnson’s invitation that he would have a significant challenge on plate: Johnson himself.

Geidt’s predecessor, Sir Alex Allan, had quit after Johnson overruled his inquiry concluding that Priti Patel, the Home Secretary, bullied Whitehall staff and had “not consistently met the high standards expected of her”.

Geidt’s time in Number 10 would come to be defined by frustration over Johnson’s failure to uphold basic standards in public office, and a disdain for the Ministerial Code.

One month into the role, Geidt concluded that Johnson had acted “unwisely” over the funding of his flat in Number 11, saying it “shook my confidence precisely because potential and real failures of process occurred in more than one part of the apparatus of government”.

In his annual report into ministers’ interests, Geidt said there was a “legitimate question” about whether Johnson receiving a fixed-penalty notice by the Metropolitan Police constituted a breach of the Code – a matter of resignation.

It prompted Johnson to clear himself of any wrongdoing. Shortly after, the Cabinet Office published a watered-down version of the Ministerial Code which blocked the ability of Geidt to initiate his own probes into codified breaches, despite calls from the Standards Committee for this to be added.

On Tuesday, Geidt appeared in front of the Public Administration and Constitutional Affairs Committee, expressing “frustration” over the PM’s conduct during the Partygate scandal.

A day after speaking to MPs, Geidt would announce his decision to resign with a terse statement. What was clear was that he had had enough of overseeing the plummeting standards of Johnson’s administration.

In his resignation letter to the Prime Minister, Geidt claims he called it quits over a potential future decision related to the Trade Remedies Authorities.

But he also said he was placed in an “impossible and odious position”. “The idea that a prime minister might to any degree be in the business of deliberately breaching his own code is an affront”, he said.

Geidt is the second ethics adviser to leave the role under Johnson. It further complicates the PM’s attempt to reset his premiership following last week’s no-confidence vote, and amid next week’s by-elections in Wakefield and Tiverton and Honiton.

William Wragg, chairman of the Public Administration and Constitutional Affairs Committee, said: “To lose one adviser on ministers’ interests may be regarded as a misfortune. To lose two looks like carelessness.”

Labour’s Chris Bryant said. “He was a decent man working for an indecent prime minister. He thought he could discreetly bring about incremental change but he was repeatedly lied to by Number 10.”

With Geidt gone, the quest for a new ethics tsar begins. It is unclear who it could be, although the last recruitment process took five months. Johnson will soon be investigated by the Privileges Committee into whether he deliberately misled Parliament. Which begs the question: who would be brave (or foolish) enough to take up such a post?