No 10 has stressed that it is “not compulsory” to wear a mask while ill after a Cabinet minister said it was “sensible” to do so if travelling.

Professor Susan Hopkins, chief medical adviser at the UK Health Security Agency (UKHSA), issued advice on Monday saying adults should “wear a face covering” if they have to leave the house while feeling unwell.

Downing Street said the advice from health officials was “longstanding” but stressed it was “not mandatory”.

Transport Secretary Mark Harper, when asked on LBC about whether he would follow such advice, said that “wearing a mask is very sensible if you are ill”.

No 10 was asked a similar question about whether Rishi Sunak would consider wearing a face covering while feeling under the weather.

But the Prime Minister’s official spokesman said he had not put the question to Mr Sunak.

“I imagine it is down to individual circumstances,” the spokesman told reporters.

The UKHSA handed out the advice this week in a bid to counter high levels of flu, Covid-19 and invasive Strep A disease (iGas).

Mr Sunak’s spokesman, asked for the Government’s opinion on the UKHSA’s guidance, said: “Obviously that’s advice they put out.

“I think that is pretty longstanding advice.

“It remains health advice to the public — it is not mandatory. People need their judgment.

“Certainly people will continue to use their good sense, having spent a long time dealing… with these kinds of infectious illnesses.”

Questioned whether it was really “longstanding” advice for people to wear face coverings if they are battling a cold, the No 10 official replied: “That’s not what the advice says.

“What you’ll see is, as has often been the case, if people are ill, they are advised to stay at home.

“Obviously people can choose to wear a mask if they wish to. It is not compulsory.

“This is advice from UKHSA rather than government ministers telling people what to do, as we saw during the height of the pandemic before the emergence of vaccines.”