Dominic Raab has insisted that the government “always acts ethically”.
His comments came following the resignation of Lord Geidt, the second ethics adviser Boris Johnson has lost in less than three years.
The senior civil servant dramatically announced his departure with a brief statement on the government’s website.
He said: “With regret, I feel that it is right that I am resigning from my post as independent adviser on ministers’ interests.”
His resignation comes just weeks after he said the prime minister had a “legitimate question” to answer over whether he breached the ministerial code over partygate.
He said the fixed penalty notice issued by the Metropolitan Police for breaking lockdown rules might have constituted a breach of the “overarching duty within the ministerial code of complying with the law”.
In response, Johnson said that the fine “did not breach” the code as there was “no intent to break the law”.
And appearing before MPs on the public administration and constitutional affairs committee on Tuesday, Lord Geidt failed to deny that he had considered resigning over Johnson’s response to partygate.
“I am glad that the Prime Minister was able to respond to my report and in doing so addressed aspects of the things about which I was clearly frustrated,” he told the committee.
“Resignation is one of the rather blunt but few tools available to the adviser. I am glad that my frustrations were addressed in the way that they were.”
Sir Alex Allan also quit as ethics adviser in 2020 after the prime minister refused to accept his finding that home secretary Priti Patel had bullied civil servants.
Asked on Sky News whether the government always acted ethically, Raab said: “Yes I do, I think we’re doing our best for the country.
“I think you’ve seen that through the pandemic with the vaccine rollout, I think you’ve seen it with getting the economy back up and running.
“I think you’ve seen the moral leadership the Prime Minister has shown on Ukraine.
“Do we make mistakes? Look, it happens, we’re human, we’re fallible.
“But actually in relation to partygate, the Prime Minister held up his hands, he’s apologised, he’s overhauled Number 10.”
Raab said Downing Street would give a further update on Lord Geidt’s departure later today, but said earlier in the week the civil servant had talked to officials about staying in his post for another six months.
“First of all, he’d been engaged with the Prime Minister in Number 10 this week and discussing staying on for six months,” Raab said. My understanding was that he was committed to the role.
“I think he had a pretty rough grilling by MPs this week, I think sometimes we in the media and as politicians maybe underestimate how civil servants feel with that kind of scrutiny.
“And thirdly there was a particular issue, a commercially sensitive matter in the national interest, which he was asked to look at.
“I don’t know which aspect of this – there will be an update from Number 10 later.”