We know that coronavirus infections are driven by ‘superspreader’ events. The majority of people infect no one, while some can infect 10s of others. Roughly 20% of people are responsible for 80% of infections. Control these events by preventing mass gatherings, and you can generally reign things in.
It looks like that failed to happen in other parts of Europe this summer. Spain had supposedly strict face mask rules but also reopened nightclubs, weddings had limits of 150 guests +, indoor social / family gatherings were far more lax. Their hospitalizations have risen considerably in the last few days.
In France, there’s also this recent case of a 250 guest wedding where 76 people were infected:
www.newsweek.com/almost-one-third-attendees-250-person-wedding-infected-coronavirus-1527469
Of course not everyone has been following the rules in the UK, but I think the benchmark guidance here - ‘6 people outdoors’, ‘two households indoors’, ‘30 people at a wedding’ - has greatly reigned in people’s sense of what is permissible. So even if people deviate from it, it’s not significantly so.
It’s too early to be self-congratulatory. In particular, school openings can yet be our undoing. But I think this is one possible explanation for why we haven’t seen the spikes that other countries are experiencing.