Dr Hilary Jones has warned that "a lot of caution" is needed over recent reports of covid-19 immunity.
Appearing on Good Morning Britain today with Lorraine Kelly, he addressed the suggestion.
"They're saying a third of healthy people with no symptoms of coronavirus could have immunity," Lorraine said. "Now what do you think about this?"
However, Dr Hilary responded: "A lot of caution here - it's from the Karolinska Institute in Sweden and a lot of good research comes from there."
"Sweden haven't covered themselves in glory," Lorraine pointed out.
"Absolutely not, and this is a bit of guesswork," Dr Hilary said. "It hasn't been peer reviewed - this is very early stuff.
"What they're suggesting is that in the UK, about 7% of the general population may be immune and 17% in London, but it could be higher.
"Just looking at the antibody tests, which aren't that reliable, they're looking at something called T cell immunity which is a different kind of immunity.
"They're saying that yes, up to a third of healthy people who have not had symptoms could have T cell immunity, conferring against covid-19 protection in the future. For how long, we don't know.
"So yeah, up to a third, they are suggesting. It's only a suggestion - we don't know of T cell immunity confers protection at all."
*Good Morning Britain airs weekdays at 6am on ITV
