Part of the problem in the south east of the UK is that if you need to divert to your primary flight plan diversion, but they won’t accept you, ATC end up saying “you know what you need to do”. We shouldn’t be having to call MAYDAY just to play the game to get to our nominated diversion and it goes somewhat against the convention of the standard phraseology regarding minimum fuel states. It’s not ATC’s fault and they’re always excellent. These days I always carry fuel to cover a non London alternate. It’s just not worth he stress.