The main part of my argument above is that you pulled that number out of your ass, you didn't address any of my points against why that number is baseless, yet you continue using the number.
Your number is a worst-case "cost" of doing absolutely nothing and just letting people die, and then you say that your suggested strategy of dumping cash on the population is much cheaper. While true in itself, the error is that you're equating the UK strategy with the worst-case doing-nothing strategy, and that therefore your strategy is better.
The case for the UK strategy is that by letting the virus spread uncontrolled through the not at risk population, health care systems won't ever be overwhelmed, death rates will be much, much lower than current measured ones, and you'll emerge on the other side with a herd immune population, without doing too much damage to your economy, and the at-risk population won't ever get infected in the first place. And by doing that, the total death toll will be lower, than having the virus slowly go through the entire population, at-risk or not.
Sounds excellent. Did we remember to tell the virus?
The point isn't to actually shut down the entire economy.
The point is that when you are talking loss numbers in the trillions, interventions that cost hundreds of billions or even "smaller numbers of trillions" to avert the big losses make economic sense; helicopter dropping a trillion dollars to allow people besides tech workers to self-isolate and socially distance themselves for a few months could be cheap, in the long run.