Companies will be told to identify poorly ventilated offices, factories and warehouses, in new guidance that will suggest that organisations buy carbon dioxide monitors to assess the risk of Covid-19 transmission in workplaces.

Government guidelines due to be issued this week are expected to tell employers to find areas in which staff are working with insufficient fresh air and reduce the risk of infections by opening windows or installing ventilation systems which draw in air from outside.

The guidance is intended to help companies prepare for the safe return of workers as Boris Johnson prepares to withdraw the "work from home" advice, as part of the fourth step of his plan to lift Covid-19 restrictions.

A No 10 spokesman said Boris Johnson would use a press conference on Monday to set out the plans and "urge the public to continue to use their freedoms responsibly, so we do not put at risk the progress we have worked so hard for.”

The guidance for companies will be finalised early this week after ministers sign off on the proposed set of changes on Monday ahead of Mr Johnson’s address.

A separate pilot project is trialling the use of carbon dioxide monitors in classrooms.

Last year, a paper produced by Sage’s Environmental and Modelling Group concluded that measuring elevated levels of carbon dioxide – emitted when people exhale – would be an effective way to spot if air flow levels have reached a level where the coronavirus is more likely to spread.

The new guidance on safer working is expected to point out that carbon dioxide monitors can help to identify poorly ventilated areas.

The document is expected to refer to advice by the Health and Safety Executive, which states: "People exhale carbon dioxide when they breathe out. If there is a build-up of CO2 in an area it can indicate that ventilation needs improving."

The Health and Safety Executive recommends non-dispersive infrared monitors, which can cost as little as £50 or as much as hundreds of pounds.

The watchdog states that the devices can be "well suited" to monitoring air quality in larger office and meeting rooms, classrooms, restaurants and bars.

Areas that should be monitored include those in which people work without mechanical ventilation, such as air conditioning, or natural ventilation, such as open windows, doors or vents.

"You can improve natural ventilation by fully or partially opening windows, air vents and doors," the Health and Safety Executive says, while air conditioning which "draws in fresh air", as opposed to recirculating air from one room to another, can also provide adequate ventilation.