With more workplaces expected to reach higher capacity as schools reopen and lockdown eases, the firm is encouraging office managers to review ventilation setups and “consider all necessary action” to ensure staff safety amid the Covid-19 pandemic.

Most offices in town centres and business parks built since the 1980s have heating, ventilation and air conditioning (HVAC) systems that recirculate existing air – designed to improve energy efficiency – rather than more sophisticated systems that pipe in fresh air from outside. This is a “common misconception” among staff, the firm said.

Bosses have opened windows to improve air flow this summer, while scientists continue to debate if stagnant indoor air caused by poor ventilation increases the risk of infection.

Laura Mansel-Thomas, partner at Ingleton Wood, said: “Winter is coming and windows are closing – putting the lockdown spotlight for the first time on ventilation for office workers, managers and landlords. What do we have? Is it fit for purpose in a global health pandemic?

“These are important questions we should all be asking ahead of the mad dash back to the office after six months of remote working and home schooling.

“But the fact of the matter is that most offices are not state-of-the-art skyscrapers with natural fresh air being pumped in all-year round. They are modern office blocks which have embraced energy-efficient cooling systems – usually ceiling-mounted air conditioning units – but it’s a common misconception that they are providing fresh air.

“As a result, workers could be potentially subjecting themselves to a build-up of infected droplets caused by poor ventilation, although we know this is a hot topic of scientific debate.”

The World Health Organisation acknowledged last month that so-called airborne transmission “cannot be ruled out”.

It could cost tens of thousands of pounds for employers to replace HVAC units with systems that pump in fresh air – and they would foot the bill even if they’re renting. Work could take months and might not be required if a COVID-19 vaccine is found, adding to the confusion.

Ms Mansel-Thomas added: “Employers are responsible for the safety of their staff and natural ventilation methods seem to have worked well this summer.

“But we have seen very little public health advice for the winter other than keeping windows open. Clearly there is no guarantee that employers will do this. In addition, minimising the risk of infection could involve radical redesigns in some cases of how offices function.

“That’s why we’re calling for all employers to review their ventilation systems and seriously consider all necessary action to ensure that their workplaces don’t recycle air that could potentially carry COVID-19 – whilst being open and honest with staff and visitors too.”