Ministers were on Wednesday reported to be planning to ditch the order to wear face masks in shops and public transport after July 19 and replace it with guidance, effectively leaving it up to personal choice.
But Mr Khan believes it is important to continue to “follow the science” which indicates masks inhibit the transmission of Covid.
He also believes masks give Londoners confidence to return to the TfL network, at a time journeys are only at 60 per cent of pre-pandemic levels.
A nationwide survey by Transport Focus and London TravelWatch last week found that 62 per cent of respondents said they wouldn’t use public transport unless fellow passengers were required to wear face coverings.
London TravelWatch has also found increasing levels of concern among travellers, with 29 per cent of London bus passengers dissatisfied with observance of the mask rules by their fellow passengers. On the Tube, only 65 per cent of passengers say they are satisfied with the amount of mask-wearing.
About half of Londoners say they would only be happy for the social distancing requirements to be removed if masks were still required on public transport. Nationally, 43 per cent of passengers said they would always wear a face covering on public transport even if it is not a requirement.
A spokesman for the Mayor said: “On the continuing wearing of face masks, it is important that we continue to follow the science around the extent to which they limit transmission on transport and in busy indoor spaces.
“Evidence shows that the wearing of facemasks gives many Londoners the confidence that they can travel safely on public transport.
“People feeling confident they can travel on our tubes, buses and trains as they get busier will be a vital part of encouraging more people into central London as restrictions are lifted further, and it is something that we will continue to look at closely.”
Emma Gibson, director of London Travelwatch, said: “Our weekly research is showing that nearly two-thirds of people say that they won’t use public transport in London unless people are wearing face coverings.
“And over 40 per cent said that they would continue to wear a face covering on public transport, even if they didn’t have to.
“This shows that along with social distancing, wearing face coverings is a really important factor for many people to feel safe on public transport.”
TfL says compliance with the current face mask rules is generally “very high”, particularly during the rush hour, with 90 per cent of passengers saying they wear a covering.
By the end of May, TfL enforcement officers had stopped 188,324 passengers not wearing a face covering or not wearing it correctly.
Of these, 12,176 were refused travel and 3,647 £200 Fixed Penalty Notices were issued.
A total of 1,448 of these fines were paid within 14 days (at a reduced fee of £100) and 121 were paid within 28 days.
Since March 16, 214 cases have been listed in court, with 30 defendants pleading guilty to the offence of not wearing a face covering, resulting in fines averaging £516. A total of 144 defendants had their case proved in their absence due to not responding to the court summons.
In one case listed in April, a defendant was found guilty and ordered to pay a fine of £1,730, prosecution costs of £450 and a victim surcharge of £173 – a total of £2,353. The defendant was also ordered to pay his own legal costs.