New guidance on face coverings should be highlighted in a campaign to raise awareness of the shift in policy, an expert has said.

A message such as ‘my mask protects you; yours protects me’ could help the public understand why it is important to wear face coverings, said Trish Greenhalgh, professor of primary care at the University of Oxford.

The Government’s road map for helping Britain exit lockdown states that people should wear face coverings when they are in “an enclosed space where social distancing isn’t possible and where you will come into contact with people you do not normally meet”, for instance in some shops or on public transport.

But unless at least six in 10 people – preferably nine in 10 – wear face coverings in public then the measure may not be enough to bring down the levels of people spreading infection, Prof Greenhalgh, said.

It comes as NHS leaders said that there should be an emphasis that a face covering is not the same as a surgical mask or respirator – which need to be prioritised for frontline health and care staff.

Prof Greenhalgh told the PA news agency: “I’m calling for a public information campaign to accompany the policy change.

“The face coverings policy was welcome but it’s expressed in very vague terms – ‘consider’ wearing a covering ‘if you can’, and only very vague suggestions about when and where to do so.

“There is also an incorrect statement in the guidance – ‘the evidence suggests that wearing a face covering does not protect you’. This is not true: there is some but not complete protection of the wearer. They also say ‘it may protect others’, which is weak: there is good evidence that it will protect others.

“Unless at least 60%, and preferably 90%, of the public are wearing face coverings in crowded places, the effect on disease transmission will be pretty small.”

Prof Greenhalgh said that for an effective campaign there must be a clear and unambiguous message to members of the public.

Meanwhile, Saffron Cordery, deputy chief executive of NHS Providers, which represents NHS Trusts, said: “It is welcome to see that the Government is encouraging further safety measures.

“However it is extremely important to acknowledge that a face covering is not the same as a surgical mask or respirator, used by health and care staff.

“These top end fluid repellent masks must continue to be prioritised for the front line as they are key to safety and to avoid the spread of the virus.

“Additionally, due to huge global demand, there have already been challenges in securing the supply of masks.

“That’s why the Government must ensure that [the] announcement doesn’t potentially jeopardise NHS mask supply.”