The two-metre social distancing rule was a "political decision" and requires a "more nuanced" understanding, a scientist advising the Government has said.
Professor Shaun Fitzgerald, who sits on the environmental working group of the Scientific Advisory Group for Emergencies (Sage), suggested people should be equally mindful of the length of time they spend near others as they are of the precise distance.
It comes as Government scientists search for methods to reopen the hospitality sector without allowing coronavirus to bounce back.
The two-metre stipulation is arguably the main obstacle to pubs and restaurants – a crucial sector of the economy – beginning to trade again.
Standing back-to-back, ordering remotely and sitting at tables only with members of the same household are among measures that have been proposed.
"The risk you are exposed to is a function of distance and how long you have been exposed at that distance," said Prof Fitzgerald, a visiting professor of engineering at Cambridge University.
"So a fleeting instance where you have been within two metres of somebody is nowhere near the same risk as face-to-face for 15-20 minutes with that person.
"So it may be time for a slightly more nuanced approach, an interpretation of what we mean by two metres.
"It is a political decision, whatever distance it is."
His comments were supported by Professor Catherine Noakes, who sits on the main Sage committee and said: "Two metres isn't a magic distance at all.
"I think people get very hung up on two metres. It's all about the context – the amount of viral load that you get."
However, neither expert is yet calling for the rule to be relaxed, a move Boris Johnson said on Wednesday that he would like to be able to allow.
Prof Noakes described pubs as "a difficult challenge" because they can be crowded, but added that the situation may be helped as the nation eases out of lockdown during warm weather.
She said outdoor transmission is believed to pose "a much much lower risk, so any operations which can move outdoors temporarily is a really good starting point".
Prof Noakes added: "I think it is worth thinking about being creative about how you design spaces, because the highest risks are where people are face-to-face and therefore have a direct exposure to the immediate [virus] droplets and aerosols."
Mr Johnson echoed the sentiment at the daily Downing Street press conference, urging people not to hold gatherings between households inside due to the expected rainy weather.