Many of us (including essential workers) are still having to take public transport to get to work - months into the pandemic, many people still seem unaware of how ventilation can reduce the spread of covid-19.

The government have recently published advice on the importance of fresh air:

https://www.gov.uk/government/news/new-film-shows-importance-of-ventilation-to-reduce-spread-of-covid-19

Public transport in London should have signage and announcements encouraging windows to be left open so everyone can stay safe. This will raise awareness and avoid members of the public having to argue the case with strangers. 

Transport companies around the country are already doing this - Sadiq Khan and TFL should coordinate this across the capital to protect their staff and members of the public.