I'd be interested in other people's experience of this.
My teenage children know a fair number of people who've recently returned from countries on the quarantine list and almost none of them, including the parents (one of whom I'm sure is a doctor), are sticking to the quarantine rules!
I would never think of reporting them, but aren't they asked to supply contact details and then risk being randomly checked over the 14 days (incurring a £1000 fine if they break the rules)?