This post is about where you have to wear a face covering. If you feel the need to discuss whether people are or should be wearing them, here's a diversionary comments box for your personal opinions.comments
In England we all know that face coverings should be worn...
• on public transport (from 15th June)
• in shops (from 24th July)
But that's just the high-level public-friendly description.
Legislation exists which more precisely defines what is and isn't allowed. Whether it's precise enough is a very good question.
A face covering is defined as "a covering of any type which covers a person’s nose and mouth", which is both very specific and fantastically vague. A list of "reasonable excuses" is duly provided. But the key thing here is the definition of "relevant place".
Part 1 of the Schedule lists categories of business premises deemed to be "relevant places" (including shops, enclosed shopping centres, banks, building societies and post offices) and also lists legal exceptions (including restaurants with table service, public houses, libraries, cinemas, bingo halls and massage parlours). An enclosed shopping centre is further defined as "a building containing shops having frontages to an arcade or mall or other covered circulation area" because legislation is often little more than a branching tree of clarification.
It's clear that stations, airport terminals and ferry terminals count as transport hubs. It's not explicitly stated that bus stations or cable car terminals count, but public transport services are defined as "any service for the carriage of passengers from place to place which is available to the general public" so I guess they do. As for station platforms, tram stops and bus shelters... well, let's dig further.
An essential feature of transport hubs is that the legislation only applies to "any enclosed part". A further sub-definition is required, and this piggybacks on existing legislation.
This covers a lot of stations, especially tube stations and mainline termini. Once you walk through the entrance into the enclosed building, it's masks on. But you can no doubt think of several stations, perhaps in the suburbs or rural areas, where you don't need to walk inside anything to access the platforms, in which case your mask only needs to go on when you step aboard the train.
In short, if it has a roof and at least half the perimeter is wall then you have to put your mask on.
A waiting shelter on a railway platform probably counts. An open platform probably doesn't, even if it has a canopy across the top. A bus station might or might not count, depending on the design. The more walls your bus shelter has, the more likely that it's substantially enclosed.
These definitions are all based on legislation introduced when smoking was banned in public places, so you might assume that mask-wearing simply boils down to whether smoking would be legal or not. Not so. Back in 2007 National Rail chose to ban smoking across the entirety of their estate, not just the enclosed and substantially enclosed bits.
In 2020 TfL have again chosen to apply the rules on face coverings to all their stations and platforms, open or otherwise, as part of their conditions of travel. Stickers at every entrance make this clear, as do printed notices signed off by the Commissioner. TfL have additionally insisted that face coverings attach behind the ears or tie behind the head, which is noticeably stronger than the national legislation. Their byelaws, their prerogative.
National Rail are a little less presumptive, and only refer to "enclosed areas".
If I've understood this correctly, at fully enclosed stations like St Pancras or City Thameslink you need to wear a face covering at all times. At stations like Clapham Junction you need to wear your face covering in the ticket halls, on the footbridges and down the stairs but not on the platforms because they're not "substantially enclosed". At fully outdoor stations like Berney Arms, Castle Bar Park and Haydons Road, however, you don't need to cover your face at all. Obviously if you're about to get on a train you're going to have to wear a mask for that, but legally speaking there's no need beforehand.
I'm less certain what the situation is if you want to walk through a station without travelling anywhere. I walked across Star Lane DLR station on the day the legislation came in, using it as a footbridge to avoid a five minute detour. The walkway is open to the sky, so not enclosed and not legally restricted, but I still passed TfL warning stickers at both ends.
In short the legal position is that face coverings must be worn in "relevant places", and the more you drill down into what a relevant place actually is the more uncertain it becomes. But if you stick to the headlines about always wearing them on public transport and in shops, you won't go far wrong. Don't start measuring the walls and arguing that you know better.