When I go into pretty much anywhere at the moment I check in by scanning the QR code. Say I am in a cafe, I then sit at a table away from other people, have my drink, then leave without getting near anyone. I do this at 2pm, for example, and am checked in on the app until midnight.
Someone else who was in the cafe that day, maybe at the same time as me, maybe not - but regardless I didn’t get within 2 metres of them - tests positive. Do I then have to self isolate? Because that makes no sense to me.