Dr Hilary Jones has warned the public to "not do what the politicians are doing" as face masks become compulsory in shops.
The TV doctor, 67, appeared on Good Morning Britain and issued advice to viewers following confusion on the new guidelines.
Health Secretary Matt Hancock confirmed on Tuesday that face masks would be compulsory in shops from July 24.
He also warned that face coverings would be required until scientists developed a successful vaccine which is unlikely to be available before mid-2021.
Speaking to GMB hosts Charlotte Hawkins and Adil Ray, Dr Hilary said: "Don't do what politicians are doing, do what doctors and nurses are doing.
"Wear a mask, if you can't socially distance in a public indoor space. Full stop."
His comments came after Cabinet Office minister Michael Gove was pictured not wearing a mask in Pret A Manger - even though he previously said that it was "good manners" to wear a mask.
He had also sparked confusion by earlier suggesting that face coverings would not become compulsory.
Hancock was probed about the Pret incident on Sky News and said: "You do need to wear a face mask in Pret because Pret is a shop.
"If there's table service, it is not necessary to have a mask. But in any shop, you do need a mask. So, if you're going up to the counter in Pret to buy takeaway that is a shop ... but if you go to your local pub you can't go to the bar."
However, a spokesperson for the prime minister later gave another explanation, saying: "We will be publishing the full guidance shortly but my understanding is that it wouldn't be mandatory if you went in, for example, to a sandwich shop in order to get a takeaway to wear a face covering.
"It is mandatory ... we are talking about supermarkets and other shops rather than food shops."
*Good Morning Britain airs weekdays at 6am on ITV
