Boris Johnson was accused of “silencing” two of the Government’s top coronavirus advisers after blocking questions about the Dominic Cummings controversy at the daily Downing Street press conference.

The Prime Minister was peppered with questions about his decision not to sack his chief aide, who Durham Constabulary said may have committed “a minor breach” of rules when he drove to Barnard Castle under lockdown, during the Thursday evening address.

But Mr Johnson said he wanted to “draw a line” under the Cummings affair, and said he would not allow Government chief scientific adviser Sir Patrick Vallance and chief medical officer for England Professor Chris Whitty to answer questions on the row to “protect them” from a “political argument”.

It was their first appearance at the daily Downing Street briefings since before the Cummings story broke at the weekend, although they were seen leaving Downing Street shortly before the press conference on Monday.

Responding to the Cummings kibosh, Liberal Democrat MP Layla Moran wrote on Twitter: “Seems the Government has gone from listening to the science to silencing it…”

Speaking to the BBC’s Laura Kuenssberg, who raised the issue, Mr Johnson said: “I know that you’ve asked Chris and Patrick but I’m going to interpose myself if I may and protect them from what I think would be an unfair and unnecessary attempt to ask any political questions.

“It’s very, very important that our medical officers and scientific advisers do not get dragged into what I think most people would recognise is fundamentally a political argument.”

Mr Johnson jumped in again when questions were aimed at Sir Patrick and Prof Whitty about Mr Cummings, telling the Downing Street briefing: “It’s very important our advisers are protected from being dragged into political controversy.”

Asked by Sky News’ Sam Coates if they were comfortable with the PM telling them they could not answer questions about Mr Cummings – suggesting a “nod or a shake of the head” would affirm – Prof Whitty replied: “The desire to not get pulled into politics is far stronger on the part of Sir Patrick and me than it is in the Prime Minister.”

Sir Patrick added: “I’m a civil servant, I’m politically neutral, I don’t want to get involved in politics at all.”

The Prime Minister later refused to answer when asked if he would have any criticism of Mr Cummings’ actions amid concerns some people would see it as carte blanche to dismiss lockdown measures.

Labour leader Sir Keir Starmer said the experts should not have been blocked from answering the questions, and said if he were prime minister Mr Cummings would have been sacked.

He said: “Nobody should be stopped from answering questions from journalists. But it’s the Prime Minister here that’s an issue.”

He continued: “We want transparency here, we want to know what their view is.”

Sir Keir said: “We’ve had a distraction of a week when we should have been focusing on the easing of restrictions and doing that safely.

“Instead it’s been wasted because the Prime Minister has been frankly too weak to draw a line under this and take the necessary action.”

Labour MP Bill Esterton said: “The public can see that the Prime Minister won’t let his officials answer questions about Cummings.

“This is further undermining trust in the government and more to the point in the advice that’s needed to keep us safe.”

Ian Murray, executive director of the Society of Editors, added: “Concerns have already been raised by the Society and others on the wisdom of Number 10 deciding which media questions will be answered and which not during this current debate.

“It is unfortunate that there appears to still be a tendency to act in a manner that might be seen by some as attempting to control the message.

“While scientific and medical advisers may not wish to answer what they might consider political questions, that should surely be a matter for them.”