Fair enough. My experience of doing it is also pretty limited but, as I said, on the occasions I've done it, it has not been a problem in terms of the capacity of the terminals. However, I probably wouldn't even try it with a 'shallow' back box!As I said, my experience with adding or modifying existing domestic installations is slim, and rarely have I come across a socket and pattress that can easily accommodate four conductors.
As you will have seen from my subsequent comments, the usual reason for people saying that one shouldn't have two spurs from one socket is not about space or terminal capacity but, rather, is in relation to having a large load 'at one point' on a ring circuit. However, as I said, the same people often don't have a problem with spurs from each of two sockets which are a couple of inches apart on the ring!
There you go ... I doubt that many here would be comfortable doing anything with a 240mm² conductor, even at midday! Horses for courses!But you'd be amazed where I can make three 4-core 240mm² cables fit where they shouldn't be able to fit at 3am in the morning... So maybe I'm just a bit soft when it comes to a plastic socket!
Kind Regards, Joh