Really not sure if lockdown's coming now, Johnson used a ton of political capital denying it, and a second policy u-turn in so many days would be disastrous for him. Even if he thought his administration could take the hit, may well have decided they lack the resources to enforce it.
If they're not gonna lockdown, they've gotta shutter pubs, coffee shops and restaurants (many are shutting down themselves but far from all), close the tube to general use, and institute a mass testing, tracing and quarantine programme.