Ex-cabinet secretary Lord Sedwill said briefings coming out of Downing Street amid the exits of two of the Prime Minister’s closest aides have been “detrimental to good government”.

Both the Prime Minister’s de facto chief of staff, Dominic Cummings, and his top spin doctor, Lee Cain, have left Number 10 following a bitter feud at the heart of Government, with the pair working on specific projects from home until they formally relinquish their jobs in the middle of December.

In the vicious briefing wars that have taken place since the turmoil became public, allies of Mr Cummings and Mr Cain had been accused of calling Boris Johnson’s fiancee Carrie Symonds “Princess Nut Nuts”.

Lord Sedwill, giving evidence to MPs on Tuesday, said the off-the-record commentaries given to newspapers, which have come while ministers are tackling the coronavirus pandemic, have been “damaging to the administration”.

The former head of the Civil Service made links between the current situation in Downing Street and when he intervened to criticise the anonymous sniping at Theresa May’s former Europe sherpa Olly Robbins during her government’s Brexit negotiations.

He told the Public Administration and Constitutional Affairs Committee: “The main point was to try and get… everyone inside government to realise this was not just unpleasant for the individuals concerned – of course you’ve mentioned civil servants there – but as we’ve seen only in the last week or so, briefings against ministers, briefings against special advisers, against other leading personalities involved with or in government is a regrettable feature of modern political life and it is detrimental to good government, whoever is at the wrong end of it.”

But he added: “When it is anonymous, there is a limit to what one can do.

“There is a lack of discipline, I’m afraid. And people do indulge themselves and it is going to take a shift in the consensus about the way politics operates in order for it to cease and for us to return to a healthier means of operating.”

Lord Sedwill said that, just as he believed he was briefed against by those on both sides of the Brexit debate while in his former role, he suspected “some of the attacks on Lee Cain are as a result” of his standing as one of the key players in the Vote Leave campaign.

But Lord Sedwill told MPs he did not think the dual departure of Mr Cummings and Mr Cain would have had much pick-up outside of Whitehall.

The 56-year-old, who reportedly had a difficult relationship with Mr Cummings when they worked together in No 10, said “advisers come and go in government” but that he did not have “any more insight” to give on the pair’s exit.

“It is a big story within the Westminster and Whitehall village, I’m not sure it is a big story in the rest of the country, but it is obviously a significant political story, and we’ve seen the same with other advisers in the past,” he said.

Meanwhile, the ex-national security adviser told the committee that no-deal Brexit preparations, which he said aided understanding of how the country’s supply chains worked, helped the Government during the coronavirus pandemic response.