Uk tactic looks very sensible to me. They will institute a lockdown long before that. But they recognize a lockdown for a prolonged time is very challenging in itself and there aren't many good reasons to be doing it too early.
Waiting until the problem obviously seems like a real problem is exactly what crushed cultures under epidemics in the past.
And yes South Korea and China seem to have stopped the pandemic in their countries, and have done an impressive job at it, but its early days and not at all clear how sustainable their approach is, or whether that approach would work everywhere.
It is too late for stopping it and you can barely delay it either.
You delay a few days or maybe 1-2 weeks if stringent but it won't be as effective when you desperately need it to be. Likely more will die if you start too early.
Think about something akin to some sort of nuclear reactor with control rods up you've just started to insert.
Thank god.
Especially where our knowledge is imperfect and subject to a lot of latency, we have to accept that we have very little actual control over how quickly the curve speeds or slows. Thus the bell-shaped curves.