My take on this is as follows. I am NOT an epidemiologist, but then I chose to train as an engineer instead. I am not a sociologist, nor an economist either, but I don't think that bans me from having an informed opinion.
I've put a spoiler on it only because it's long, which is my style, and looks at lots of points, which is also my style, and is not tabloid-worthy and so can make for tedious reading if you just wanted a soundbite to dig your teeth into, which is also my style.
All we get is "official advice", which is UK.gov pushing out soft messages that they hope will have the desired effect, once interpreted by the various levels of the press and digested by us and our comrades. And we all see things differently.
Gov.uk has chosen the "herd immunity" path. This, it is hoped, will build up a general resistance to the disease so that, eventually, Covid-19 will be just like any other flu, part of the panopticon of endemic afflictions within our (UK) society. This will, eventually, offer the best protection to vulnerable people, as well as be the most manageable within the NHS, and within the wider economical and societal structures within the UK.
To get to a viable herd immunity, most of us do need to catch this disease. So put away some loo roll and dry goods for when it's your turn to take a couple of weeks away from everyone else, because it has to happen at some point.
The key to this is that it must NOT happen to us all AT THE SAME TIME. It must be spread out, so the NHS can cope as best it can with those it affects badly. And so the government is using soft-levers to try to get just the right amount of infection within communities — quick enough that herd immunity will be achieved before everyone (society) gets totally bored by this (and I'm not talking about me here — I'm happy with my own company, but many can't sit still, or feel they have the right to continue as normal), but also slow enough that the NHS can cope and so a "small" number of people will die.
And people are going to die. Most of them will be elderly, most of those will have other underlying conditions. It's going to be brutal. The difference is that it may be 200,000 people dead if the NHS DOES cope, or it may be two million people dead if they don't. Or 100,000 and five million. Or one million and two million. Who knows? But the numbers are going to be big and scary, or bigger and scarier.
That's my take on the UK.
Only UK.gov has chosen this path (at the moment). Why?
I think, and it has been suggested upthread, that it has been to do with unfettered rates of transmission and subsequent complete overwhelming of regional and country health services elsewhere around the world. Because countries were affected earlier in this pandemic then they didn't have the information or social backing to clamp down hard on it. Subsequently, their hands were forced into trying to stop all transmission completely, just so that they could cope with the infections they had at that moment in time.
Now, at some point all those restrictions are going to be lifted and, if they are lucky, then herd immunity will have been achieved as a by-product. If not then they are going to have further outbreaks and this is something that is going to run and run, until eventually herd immunity is achieved everywhere and Covid-19 becomes just background noise, like 'flu.
I think — and this is just my opinion — that gov.uk sees/saw a narrow window of opportunity to achieve herd immunity at the first attempt. Everything is geared towards that. Everyone (or at least 60-70% of us) must catch this, suffer its effects, and then be considered part of the "immune herd". But it is a risky gamble, because gov.uk has only soft levers at its disposal for any length of time — if it pulls the Hard Levers, it's not difficult to see civil disobedience trailing not far behind, because people are going to hate being cooped up. So soft levers.
Pulling soft levers is a bit like driving a hovercraft: you turn left and wait for a reaction, but you're still travelling in your old direction, while pointing in your new direction, so you give it a bit of an oversteer and extra throttle — you're constantly having to balance the amount of lever with the amount of push. And then factor in a blustery wind ... occasionally the Hard Levers need to be pulled, but only for a minimal length of time.
The recent letter from scientists to gov.uk stating that thousands of people are going to die while achieving herd immunity is absolutely correct. However, in my opinion, it fails to acknowledge the thousands of people who would die anyway if herd immunity were not achieved. I don't think there is a single correct answer here — I do believe that herd immunity, at least from a common sense point of view (I'm an engineer, not an epidemiologist, remember), is the least-worst solution, otherwise we're going to be running scared from this disease forever. But I would absolutely hate to be the one to make that call, knowing that, in all probability, I would be the one who was going to indirectly contribute to the early deaths of lots of old and infirm people, and the ire of those who have to put them in the ground, during this first phase. However, to think that we "contained" it at the outset to save thousands of lives only to have to "contain" it again and again and again, costing thousands and thousands of lives over and over, doesn't make a lot of sense.
So, it leaves me with a paradox: how to catch it and spread it, but only in small amounts, at a population level? This is where advice on hand-washing, social-distancing and "carry on but carefully" comes in — go out and spread this, but only in small amounts, please. It is totally imperfect, but possibly the least-worst, and — with a lot of luck — good enough to achieve herd immunity with manageable collateral mortality.
Which to me suggests — in all cases where you are symptom free and have not knowingly been in contact with the contagion — that going to the local shop or supermarket is fine (assuming it's not heaving when you get there, and wash your hands before you go and again when you get home), walking the dog is fine, and gathering in the spacious outdoors for a bike ride is also fine. Eating out is probably not okay, nor attending a football match in the stands, nor going to the pub to watch it on the telly either. Gathering in a village hall is questionable, although if done briefly then of no greater risk than going shopping. And stay away from old people and care homes. This ensures a steady rate of transmission through the community, hopefully just the right amount — not too quick, but not too slow either — and away from the super-vulnerable.
I'm comfortable with the idea that my current point of view is naïve or misinformed, but it's based on a fair bit of reading around and piecing things together myself. I reserve the right to change my point of view based on reasonable and rational counter-arguments, as has already happened thanks to the sharing of thoughts by others on this thread.
FWIW, Ewa and I decided to postpone the Cambridge Pork Pie and Spring Dash next weekend (21 March) on the basis that we have no confidence that we would be able to run it — either because of a ban on gatherings, or a requirement from AUK, or because either of us having to self-isolate. We would definitely not have been able to run the start/finish the way we like — relaxed, informal, all-welcoming, chatty — and for riders and for us that has become an important part of the events. Hopefully we'll get to reschedule later in the year when the bulge has passed; if not then so be it.
And I will continue to ride my bike. I live about 200m from open countryside. I haven't ever needed hospitalisation for anything, so the risk of me needing it because of an incident on the bike during this crisis is extremely low. I will ride DIY-by-GPS, or perm-by-GPS, and carry everything I need, plus the Big Bottles. I probably won't be riding another calendar event for the foreseeable — not to avoid catching Covid-19, but in case I am an asymptomatic carrier.
My point is this: we all need to catch this — just not all at the same time. And to catch it, we do all need to continue to interact with other people, just limited in order to control the rate of infection, not the overall sum of infection.