“Covid secure” perspex screens in workplaces may increase risk of virus transmission if they are placed in positions that block airflow or cause poor circulation, scientists advising the Government have warned.

In an undated document released on Friday by the Scientific Advisory Group for Emergencies (Sage), the experts said there is very little overall evidence on the effectiveness of these barriers at reducing infection transmission through droplets.

Evidence suggests coronavirus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak or breathe.

These particles range from larger respiratory droplets to smaller aerosols, according to the World Health Organisation (WHO).

Sage experts said there may be benefits to using screens or barriers in certain situations – such as where people are sitting face-to-face and less than two metres of each other.

There is some epidemiological and mechanistic evidence that suggests that screens could increase risks of aerosol transmission due to blocking/changing airflow patterns or creating zones of poor air circulation behind screens

They added: “Screens are unlikely to provide any direct benefit in reducing exposure to the virus from droplets or aerosols when people are already located at 2m or greater or where they are not face to face.

“Unless they are designed to work with the airflow, screens are unlikely to reduce exposure to virus in smaller aerosols as they can easily pass around a screen with the airflow in a short period of time.

“There is some epidemiological and mechanistic evidence that suggests that screens could increase risks of aerosol transmission due to blocking/changing airflow patterns or creating zones of poor air circulation behind screens.”

The scientists said that whether the screens are effective will depend on layout of the space, the ventilation, the size and design of the screen and the interactions that happen in the environment.

They added: “There are large numbers of screens that are unlikely to be effective due to their design or positioning.”

The experts said further research is needed to look at the effectiveness of screens and barriers in real-world settings.

They also said it is unclear whether screens or barriers can act as reminders to people to maintain social distance or help organisations manage the layout in their environments.

The experts said: “It is also possible that screens could provide false assurance, although studies have shown that there is very little evidence of risk compensation behaviour.

“Further research is needed to understand whether there are any behavioural influences of screens and barriers.”