For modelling stuff, there is also Hannants in collindale, fairly large range of military model kits there as well.
Hmm.. 4D models is on leman street, that's mainly architectural, but they have a fairly extensive tool range and various useful bits

For resin supplies and some very good sculpting tools, there is Tirantis, on Warren Street.
I'm sure I'm forgetting something, but those are a few to be going on with
Sadly, we've lost a few in recent years, mainly the ones dependant on Model Train sales.
Marc