ragged - the "everyone knows everyone else and is some way connected" took a lot of getting used to after the whole "couldn't pick out my neighbour in a police line up" lifestyle of SE London!
I'm a little cushioned from the worse of it as this is a commuter town for London having great train links, so there's a lot of 'outsiders' who don't have family connections, and the London invaders (like us) have pushed up house prices so many local people are pushed a bit further out into the villages with crapper train links. But still it's a small place, and when I fainted on the train 8 wks pregnant with DC2, told a nice lady who caught me that I was pregnant and she loudly announced it to get me a seat in first class (I'd been standing). When I got to church on Sunday, 2 different people came up to quietly congratulate me as their DH's were commuting into London offices on the same train carriage. (Hadn't even told my mum yet at that point!)
DH talks about our local "mum mafia", and it amazing that most woman are connected in some way.
OP - if you have a busy job that keeps you away from a lot of the school gate stuff, it could be equally you wouldn't fit in with a SAHM culture in an area in London, but then if you had more going on in your life, you wouldn't notice it. When you say there's nothing going on, is it just that you don't konw about it, or it's stuff that's happening while you're at work, I know certainly where I am, it's much more common for events to happen in the working day as there's a large SAHM and retired community, and if you are working FT you might well miss out. Plus as things are less well advertised and rely on 'word of mouth', if you aren't more than 'smile and nod' relations with most of the local SAHMs, then you might be missing out. 
I would say you need to put more effort in with groups, societies and trying to find a bigger group that suits you. Give yourself 6 months of being a "joining in sort" and see if you find a wider group of the community you do get on with - the school gate mums are really only a small part of any community and it's only a small period of your life when you'll come into contact with them. If after all that you don't find yourself feeling more comfortable, then look at moving to different towns/large villages in the area, London isn't an option, but there's not just "London" and a homogenious "everywhere else".