Officials at the Health and Safety Executive (HSE) suggested the time limit in guidance on how workplaces can improve ventilation and cut the risk of transmitting the virus.
However, public health experts and MPs have poured scorn on the advice, describing its proposed efficacy as “doubtful” and its introduction as “unnecessary”.
Paul Hunter, professor of health protection and medicine at the University of East Anglia, said: “In general terms, it makes sense to minimise risk and keep contact as short as possible. Whether two hours makes a real difference in terms of risk is, I think, doubtful.
“I suspect two hours was chosen mostly to do with the fact that anything important is done in two hours. Two hours is not a magical number.”
Although cases and deaths have begun to rise in recent weeks, Prof Hunter said that the expected surge in winter infections will not be “anywhere near as bad as it was last year”.
Modelling from the University of Warwick found that a winter wave would peak at about 1,500 hospital admissions a day, far below the 4,000 a day during the peak last January.
Prof Hunter added that the Government is likely to “let the virus rip” this winter, with Downing Street relying on the success of the vaccination rollout to mitigate the expected rise in cases.
Marcus Fysh, the Conservative backbencher and member of the Covid Recovery Group, said: “This is the first I have heard of two hours being something that is of any significance on a scientific basis. I am deeply sceptical that this would have any effect at all. So frankly, I would ignore it.
“It is the hospitalisations that are the key issue and the deaths that result. They seem to be tracking below what people expected to happen from this wave moving through. So I just think it’s unnecessary.
“It seems to be an extraneous thing that someone has come up with it because they wanted to be able to say something about it rather than it being meaningful in any real sense.”
The advice from the HSE also recommends that businesses install carbon dioxide monitors to give a “rough indication” of whether the natural ventilation from open windows is “sufficient”.
It adds: “Levels of CO2 creep up during longer or busier meetings. They remain high for a long period of time – even after the room has been vacated.”
Prof Robert Dingwall, a former member of the Joint Committee on Vaccination and Immunisation, said “a lot of uncertainties” remain on the evidence for aerosol transmission of Covid-19 indoors.
While good ventilation is “desirable,” he admitted that the advice was “verging on the cautious”.
Prof Dingwall said: “Good ventilation is certainly desirable, it probably makes a bit of difference. Nobody should be in a meeting for more than two hours, anyway.
“I think what one can say is this is reasonable advice, but it should be open to review as we learn more about the circumstances of transmission. You could say it is verging on the cautious, but I wouldn’t be too dismissive of it. But that’s probably because I don’t approve of meetings lasting that long.”
A spokesman for the HSE said: “Employers must make sure there’s an adequate supply of fresh air – ventilation – in enclosed areas of the workplace. HSE’s guidance helps employers identify, assess and reduce the risk of transmitting coronavirus (Covid-19) in their individual workplace setting.
“We’ve provided some examples to help employers take practical steps to improve ventilation in different scenarios. Deciding on what measures to put in place to achieve adequate ventilation depends on the specific workplace and should be part of an employer’s risk assessment.”