Sir David Lidington, who served as de facto deputy to Theresa May before Mr Johnson replaced her at 10 Downing Street, said that the public slanging match with his former senior adviser was a distraction from the prime minister’s work.
And he said that if there was any substance to allegations raised by Cummings over “unethical” and “possibly illegal” actions proposed by the PM – including shutting down a leak inquiry and getting Tory donors to pay to refurbish his Downing Street flat – they should be reported to the Electoral Commission, the head of the civil service and Whitehall’s ethics chief.
After days of tit-for-tat accusations culminating in a claim – denied by Downing Street – that Mr Johnson was ready to see “bodies pile up” to avoid a third lockdown, Sir David warned that “internecine warfare” within the highest ranks of government never ends well for those involved.
Speaking at an event to relaunch the internationalist Best for Britain campaign, Sir David said: “I clearly have not been a part of the current government, and I am in no position to comment on what actually happened in those internal negotiations.
“It seems to me that if Mr Cummings has substance to those allegations, he should report them to the relevant authorities.”
Speaking to The Independent later, the former Chancellor of the Duchy of Lancaster made clear that he did not regard any of the allegations as matters that should be reported to the police.
But he said anything of substance should be reported to cabinet secretary Simon Case, Cabinet Office director general of propriety and ethics Darren Tierney or the Electoral Commission, which has a statutory role on political donations.
Sir David added: “This sort of public battle and slanging match doesn’t help, whoever the government is. It distracts people’s energies, attention, bandwidth, away from the day job, which is what they should be focusing on.
“My view is that if you work in the senior reaches of government, whether as a minister, an official or a special adviser… you speak your mind completely frankly to those who hold power and are taking decisions, but you don’t go around trying to justify your position afterwards.
“Talking about Conservative or Labour governments, where they have had internecine warfare, it has never helped the people participating in it.”
Asked about the recent spate of rows over private lobbying of ministers by business figures including Greensill Capital adviser David Cameron and vacuum cleaner tycoon James Dyson, Sir David told the Best for Britain virtual seminar: “My view on this is that transparency is by and large the best antidote.
“Ministers are meeting senior people from business, from charities from trade unions, every day of the week. Do all those meetings count as lobbying? I’d be very worried if ministers weren’t talking to anybody outside Whitehall.”
He added: “What is important is that those external contacts are properly registered and published so that everybody can see what happens… and also that when there is a decision about letting a contract or something, that it is seen to have been done fairly according to established rules.”