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I welcome the news that London mayor Sadiq Khan is campaigning to make face mask wearing compulsory for people travelling in the capital during the coronavirus crisis. I hope other mayors and local councils will follow suit. 

I hope that Government proposals, now being discussed, to make mask wearing a plank of lifting lockdown will prevail. This revolutionary – but common sense proposal – may be ridiculed by those who would insist that there was insufficient medical evidence for such action. 

But these are not normal times. We do not have time to carry out a mass of scientific studies. We need to act now. The number of deaths due to Covid-19 each day continues to shock and the NHS, while coping, is under pressure. 

So I endorse the idea put forward this week in the British Medical Journal (BMJ) that we should adopt what is known as the ‘Precautionary Principle’. 

London mayor Sadiq Khan is campaigning to make face mask wearing compulsory for people travelling in the capital during the COVID-19 crisis

This states that we should sometimes act without conclusive evidence if this is likely to do good – and, having made a study of the evidence for and against, I believe that is exactly what face masks could do. 

Written by a team led by Professor Trisha Greenhalgh, of Oxford University, the BMJ article warns: ‘In the face of a pandemic the search for perfect evidence may be the enemy of good policy.’ 

In more than 40 years as a medical journalist – much of it working for this paper – I understand absolutely the value of evidence-based medicine. 

Former Health Secretary Jeremy Hunt has branded a move to make masks compulsory as ‘sensible’, given how social distancing can be impossible on trains and buses.

The Index Medicus, the bible of medical research, lists more than 9,000 articles and studies about the potential benefits and hazards of surgical masks I have always believed there was logic behind the idea that face masks might protect us against infection, but my experience of wearing one last month in Vietnam was revelatory. 

When we arrived in the country – before the widespread international lockdown – my wife and I weren’t wearing masks. Indeed, we were surprised when booking into our hotel in Saigon to see all the reception staff in masks. 

This had a powerful symbolic impact in addition to any protective effect. If everyone around you is wearing masks, you become increasingly hygiene conscious and cautious about what you do.