@MarshaBradyo here are my back of a beermat calculations.
The first scenario is if we go with the whole "we're not trying to stop this disease in its tracks, just all catch it at a rate the NHS can cope with." (Sorry, I couldn't think of a catchier description).
We started out with 4,000 ICU beds. Each patient needing critical care takes up a bed for an average of 8 days. Let's optimistically say they can treat 50 people in a year.
Let's be optimistic again and say that we can ramp up that provision to 20,000 ICU beds (hopefully these new CPAP machines being developed by Ferrari can help with that).
So, we have the capability to treat 1,000,000 people in a year.
5% of infected people require ICU care. So, we can multiply that (very optimistic) figure by 20 to see how many people the NHS can cope with being infected. That gives us 20,000,000 people. Of course, we won't immediately have that capacity, so let's bring that down a bit to say... 15,000,000 people.
That's a very optimistic figure, based on us having a vaccine within a year. It would still result in a large amount of deaths.
The alternative scenario is that we somehow manage to get the figures right down to near zero, control this completely within the country, test massively, contact trace rigorously and start heavily quarantining people coming into the country.
If that was the case, we might keep cases under a million in total with a massive reduction in deaths.
Note: These figures are all totally back of a beer mat. Individual parts, like the 5% needing ICU, the 8 days in ICU and the 4000 ICU beds initially are verifiable, but the figure of increased capacity being 20,000 is just me making it up.