Lord Christopher Geidt has stepped down from his position as Boris Johnson’s adviser on ministers’ interests a day after he appeared in front of a cross-party committee of MPs.

A little over 24 hours earlier, the crossbench peer declined to deny that he had previously considered quitting as ethics adviser over Mr Johnson’s response to being fined by police over partygate.

Lord Geidt was previously the Queen’s private secretary, spending a decade acting as a channel of communication between Downing Street and the monarch until 2017.

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 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.

He entered the Lords after stepping down from his role with the royal household, becoming Baron Geidt of Crobeg and sitting as a crossbencher.

Last April, Lord Geidt took on the role of ethics adviser to the Prime Minister.

He began the job 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 but it might reasonably have been expected that the Prime Minister be curious about the financial arrangements surrounding it.

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.

The ethics adviser concluded in May last year that Mr Hancock had committed a “minor” but undeliberate breach of the Ministerial Code and should not resign from his position.

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.

Last month, Lord Geidt suggested Mr Johnson may have breached the Ministerial Code after being fined following partygate.

Mr Johnson responded 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”.

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.”

Asked why, he told MPs: “I think matters relating to the code have become matters of greater profile in the public square.”

Expanding further, Lord Geidt said the “increased scrutiny on the considerations of Government ministers” accounts for the increased profile.

“It’s been an especially busy year,” he added.

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.”