Dr Hilary Jones issued a stark warning on Good Morning Britain that we are not reaching herd immunity with Covid-19.
He added that the death rate will sharply rise in the next two weeks to follow the rise in hospital cases.
He was speaking to host Kate Garraway about misconceptions that the rise in hospital rates, but not yet death rates, meant the virus is less lethal now, or that we have
He explained that people tend to be sick with Covid-19 for several weeks before they die.
"Only a few people have been exposed to Covid-19 so far, so herd immunity is not something we can rely on, we don't know if it exists at all, we don't know how long it lasts if it does exist," he said.
"If we did rely on it, it would be a massive, dangerous experiment... It means we failed to react."
Speaking about the three-tier system, Dr Hilary called for a full national lockdown.
"What happens in one region tends to be followed by what happens everywhere else, this is a national virus, it isn't favouring Liverpool or Manchester, the more people meet up, the more it spreads," he said.
"We are seeing rising numbers around the country, the south is just behind the north.
"It is the inverse to what happened earlier in the year.
"If we are going to go into lockdown I think it should be a national one, get the numbers down, get the NHS prepared, increased capacity in intensive care, we can do a lot of planning now that will help in the future.
"Rishi Sunak can say that another lockdown will cause a lot of harm, we are in a pandemic, there is going to be harm either way, in health or the economy.
"It is a tough time, we have to accept there will be pain and hard times."
* Good Morning Britain airs weekdays on ITV at 6am
