@MRex I live in London too, and have been out socialising outdoors with those outside my household, and indoors with my household, however, we have observed a lot of indoor tables that seemed to be non-households - for example two tables I saw at the weekend were exchanging gifts (which I think would be unusual for a household to do at a restaurant), so I think unfortunately there is quite a lot of non-compliance. Similarly, we were shopping and left because the streets were too crowded to social distance, and few people were wearing masks which I think should have been worn given the conditions.
Additionally, a large number of people seemed to be from “out of town” when we were shopping - purely basing this on the large queues at hamleys, number of people asking for directions and generally looking lost, I also heard a lot of Kent/Essex accents so potentially people travelled in to enjoy the lights/shops etc. from higher tier areas (or like me, they could live in London and have a non-London accent). So I think there’s a lot at play in London, combined with quite a young and social population that often don’t live with/see more vulnerable family members regularly which might encourage riskier decisions than if you knew you were going home to your parents and grandfather’s house. This could change in the next week or so, given Christmas plans.