Sweden population: 10.2 m
UK population: 66.6m
Sweden population density:25/km2
UK population density: 275/km2
Sweden largest city population: 1.5m
UK largest city population: 8.9m

Despite the obvious differences between Sweden and the UK, like us having 10 times the population density, there's really no evidence, even if cases dropped in the week before lockdown, that lockdown was pointless. Because lockdown did, in fact happen. So the idea that "just letting it run its course" would have the same outcome is just speculation, with support for the argument coming from a single country which bears little resemblance to the UK.

Look at the rest of the world, however and things look a little different.
Do you really think that allowing life to go on as normal would have resulted in fewer deaths?