If in doubt you self-isolate. The advice is now that if anyone in your household is vulnerable, you all self-isolate.
Similarly, if anyone in your household has symptoms, you all self-isolate.
For the next 12 weeks, even if no one in your family is vulnerable and no one has symptoms you still limit all social contact. Those who can should work from home. Those who can't should go straight to work and straight back home. No after-work drinks. No weekend BBQs a a friend's house. We do our work and we do the occasional food shop / online food delivery. We walk the dog or do outside exercise at a distance from others, but we do not stop to chat. It is very clear. We also make sensible decisions on physical contact with elderly and vulnerable relatives who live separately from us. If they need our support then we self-isolate so we can visit them.
The government is not forcing major events to be cancelled, but it is withdrawing the police and ambulance protection that they require. This means they cannot go ahead. They won't be insured without that, so they will need to be cancelled.
By telling people what they should do, but not what they must do, the government does not burden itself with having to arrest stupid people ignore the recommendations. On the whole, I think compliance will be sufficiently widespread for there to be nowhere for those people to go, no one for them to meet and nothing for them to do, so they will not be a risk.