Odd that you should pick on Sadiq Khan's comment for being ludicrous among all those you could have chosen.
He said that on Good Morning Britain on the 5th March. This is the very same day Boris was just floating the idea/suggestion (that of course he didn't agree with) that we could let it run through society and we might "take it on the chin".
https://www.mylondon.news/news/zone-1-news/london-coronavirus-no-risk-catching-17870746.
Anyway, Khan was naive and that comment was indeed ludicrous, even though we only had 90 confirmed infections in the UK when he said it.
He also said at the beginning of March that he didn't foresee the tube being closed or even concerts being cancelled. That hasn't aged well either.
https://www.cityam.com/coronavirus-sadiq-khan-says-tube-travel-ban-is-unforeseeable/
However, on 24th March he was apparently saying 'stop Tube travel or more will die'.
https://www.bbc.co.uk/news/uk-england-london-52017910
(Incidentally, this was the same day Boris told his subjects that they could only leave their homes to buy essential items, exercise once a day, and travel for work where "absolutely necessary" or for any medical need. No mention of masks.)
The tube was not shut but ran a controversial restricted service that some said had the unfortunate effect of concentrating passengers into fewer carriages.
I think Khan was late but has consistently called for masks to be worn since 17th April.
https://www.cityam.com/coronavirus-london-mayor-sadiq-khan-calls-for-face-masks-on-tube/
"
London mayor Sadiq Khan called on the government today to make coronavirus face masks compulsory for people using the Tube or shopping.
The mayor said that evidence from around the world was that face coverings help stop the spread of coronavirus.
“In those circumstances where its not possible for us to keep our social distance, think of public transport usage, think of when you’re in a shop, we should be using non-medical facial coverings like bandanas, like scarves, like reusable masks,” Khan told the BBC.
The government’s social distancing measures do not mention the wearing of face masks. But Khan said that should change."
I'm not a massive fan of his, but he was calling for action on masks, specifically, three months ago.
We are now in the middle of July.