Dr Hilary Jones sounded a warning on Good Morning Britain on Monday as lockdown began to ease in the UK.
He insisted that the Covid infection rate needs to be kept down and that the vaccine can't be relied on alone.
He told hosts Susanna Reid and Ben Shephard: "What have we learnt in the last few months? That we've gone into lockdown too late and we've come out of lockdown too late. So we need to be really careful.
"I hope that we don't need the police to be enforcing anything because it's an impossible job for them. I would hope that people behave sensibly and have understanding that this is the way forward.
"We can't rely on vaccinations alone because unless you vaccinate 90% of the population and you get 90% efficacy rate from those vaccines, you've still got a large amount of people vulnerable to the infection.
"So basically we make Great Britain a smaller island with vulnerable people. That's not what we want - we want everyone to be safe. So we can't just rely on vaccination.
"We can't come out of lockdown early and just abandon the rules because we still have 3,800 positive cases in the last 24 hours, 383 people admitted to hospital, possibly many of them requiring ventilation still. It's a very nasty illness."
Dr Hilary went on to hit out at people pushing to abandon lockdown and get back to normal life.
He continued: "They use figures based on the fact that the mortality rate is relatively low but it's only low because of the excellent work that the NHS have been doing."
Susanna added: "So don't take this removal of 'stay at home' as 'it's time to have a free-for-all'? There are very clear rules in operation."
Dr Hilary continued: "We need to keep the infection rate down. If we still have about 50 people per 100,000 who have got the infection, they're still passing it on.
"We're going to get new variants emerging. Look what's going on in Spain, Italy, Germany and France - they've got very high rates. And we tend to follow what happens there."
*Good Morning Britain airs weekdays at 6am on ITV
