In amongst all the hysteria, both on this forum and reflected through BBC sensationalist journalism, isn't the underlying message quite sound (at the bottom of the quoted article and as Mojo mentioned) to keep a certain level of ventilation which helps with air circulation, thereby minimising risks of transmission and even for general health in other times?
Ultimately, ventilation is one of the main issues and has been missed to an embarrasing degree in our management of the pandemic.
The evidence has been there for quite a while about airbourne transmission. The fact of the matter is, you can do as many one way systems, social distancing measures and "deep-cleaning" as you want, but the key issue is dose x time.
You need a certain level of exposure to the virus to establish an infection. It's not simply the case of 1 virus entering and causing a full blown infection. Your body can deal with that. The issue occurs when around 1000-10,000 virus particles (consider up to a million are released in each replication cycle) enter the body. Some droplets (carrying viral particles) are heavier and fall to the floor, but some are lighter and remain suspended in the air for quite some time. Outdoors, this is not an issue, as the virus particles become very quickly diluted by the massive volume of air. The primary risk of spread outdoors is those heavier droplets, with high amounts of viruses. One contact with those and you could possibly establish an infection. This might occur if you say touch a park gate someone has coughed on, or get coughed on directly, then later touch your face. (The majority of infections actually enter the body around the eyes.) So outdoors, social distancing and santisiation are quite adequate forms of prevention. In fact, passing someone on the street at less than two meters isn't that big of a deal, just make sure to wash/sanitise your hands before touching your face, and it's probably fine.
However, things get a bit messy when moving into indoors spaces. These suspended aerosols are not diluted by the air and just linger. Breathing in enough of these eventually gives you a high enough viral dose to establish an infection. Plus, given the advantage of an enclosed space and enough time, one carrier can spread to a suprisingly large number of people in the room. This is why resturants are so problematic. People sit in them for extended periods of time, without masks, and typically there is a fairly substancial number of people in there at any one time. So, with a lack of proper ventilation, this is a recipie for disaster.
Ways we can make things safer involve reducing the total number of people in a space, opening windows and reducing the overall viral load being ex/inhaled by using masks. Social distancing and sanitisation become less relavent as we move indoors.
The harsh truth is, some things are not practical to do right now. That said, I don't agree with how the government has handled this, and think that policies have missed a lot of the important details. Armed with the right information, we can move forwards and do things in a more safe manner.
Now on to what we can do about it:
Opening windows is an effective strategy, but not the only one we can use to approach reducing viral particles in the air.
Risk Reduction Strategies for Reopening Schools
This report notes that:
SARS-CoV-2 present in the coughs, sneezes, and exhaled breath of an infectious person can be transported in the air to disperse throughout a room and can remain aloft for hours. This long-range airborne virus can infect even people who haven’t had close contact with the infectious person if they inhale a sufficient amount of virus.
In some cases, it is not reasonable to bring in additional outdoor air. For example, on very hot summer days or very cold winter days it may not be impossible to maintain a comfortable temperature in the classroom if the windows are open.
It goes on to reccomending reducing air re-circulation on HVAC, as it could move virus particles from a room with an infected individual to one without, as well as improving the quality of filters on HVAC systems. (While not many UK schools have HVAC, a lot of shops and offices do, so this is worthwhile advice.) It also reccomends using portable HEPA filters, which can remove viral particles from the air. (Airlines began using HEPA filters in the 70's/80's after a number of flu outbreaks, they are also used to clean the air in hospital operating theaters.
Interestingly on bathrooms:
Finally, bathrooms can be places where crowding occurs, especially when children have shared windows of time when they can use the bathroom. To enforce physical and group distancing and to minimize crowding, it may be useful to close bathrooms during transition periods and promote bathroom breaks during class time instead, to assign classrooms to use specific bathrooms or to stagger the timing of scheduled bathroom breaks by class.
I wouldn't be suprised if schools still aren't letting kids out the class to go to the bathroom, instead forcing them to go during breaks.
The whole report is very interesting and I'd reccomend giving it a read. I think we spend so long focusing on wether we SHOULD do things, that the conversation around doing them safely is completely missed. I saw a ton of overcrowded school buses during the last lockdown, with barely any space for students to socially distance at the stops. Kinda crazy really. Same for supermarkets & shops, where poorly thought out social distancing measures are extending the periods of time people are in shops, or people are queing in an indoor space (such as a shopping centre) for a long period of time to gain entry. Really, the ques should be on the outside of the centres, rather than inside.
Mr Hancock) have just spent most of the day with my daughter who is a GP and therefore might have come into contact with the virus; as our rooms are on the small side and we were 5 altogether we had a fanlight open allowing stale air to escape. 
