The uncomfortable truth is, the British government have weighted cost and benefit, and they have decided, the death of thousands or more is not worth the cost of near-absolute lockdown of a country, It might lead to total breakdown of the economy, full-recession, and that may cost more lives anyway. These elder people are old enough anyway, and the death rate for young is just 0.2%. (which rise to 1.3% for people elder than 50, and 6% for elder than 60 according to data from China)
What does those number mean? If you and your partner's parents are elder than 60 years old, there is 25% chance, at least one of them will die. That is, very likely, you're going to hear it from your best friends that one of their parents died from COVID-19. Are you okay with that? (Under the assumption everyone will get infected anyway). And beware, these statistics are not final, and mostly from patients who received some level of medical care, although we do not yet know how many of those heavily-ill patients received intense care. Without medical care, the number could easily double, after all, it takes time to die, that's just how lung disease works.