Thank you all so much for all the replies!
Wow. You may not say much in person, but just get you in an internet forum... kidding.
I guess the general feeling I get is that, yes, if you're an expat (no matter where you come from originally), you have to make the effort, and that's what I tend to do, without forcing it. It has to come naturally, but in order to live in a foreign culture, you do have to express curiosity, we do often go exploring (yesterday we went to Leeds Castle), we make it a mission to get to know the country that we're in... and often times, I feel, that people just aren't interested. That's depressing.
Here's a bit of background to put it in context: I lived in France during summers since I was fifteen, I spent a couple of years in Italy before / after university, I worked in Ireland for a quarter and Dubai for another quarter, before we had my son. I traveled a lot. My family hold passports from the U.K., Ireland, and Israel, and (obviously) the U.S. where I grew up. ...my husband and I spent all of 2009 in France on a work project. He's German. He grew up in Namibia. ....so we have a bit of experience hoofing it all around the planet. And we always take it upon ourselves to do the adapting. But I have to be honest, there are times it feels like London is not worth the effort. it's not that the museums and the parks aren't amazing - they are - it's that you never *ever* make local friends. i'm speaking from my own experience but it's a generally acknowledged fact amongst expats.
Which leaves me wondering, why does this place suffer from so much cognitive dissonance? I mean, if you're going to invite people to come from all over the world (I was transferred here from New York by Deutsche Bank) to come and live in your city, why not enjoy it?! New Yorkers and Parisians - my two closest points of comparison - never let you get away without your life history. Their perspective is, approximately, to paraphrase: "you want to live here? (...arched eyebrow, slight frown).. okay! tell me about yourself! starting now." ...and that conversation can go on and on.
i get that not everyone does this, which is no bad thing. but i sense that there is a huge amount of resistance to the mere idea of foreigners living here, even those of us who are not chasing asylum, benefits, etc., all more problematic topics. so why not take some interest in the people you live next to, if for no other reason, than to get back some sense of control over the process?
it's ridiculous to pretend that there's some kind of Berlin wall running between our gardens. silly. and stupid. and... guess what? we're really not all that different. we all have a lot more in common with each other than anyone likes to admit. we are all a lot more fortunate than the asylum seekers who probably outnumber us, to put it in real perspective.
so forgive me, but this cultural exception might make sense if it were about a real phenomenon -- like protecting a national industry, or a national culture - like France does, to occasionally comic but serious effect. but saying, "I can't talk to another mummy at nursery," presumably because our cultures are different, when you claim to call us cousins (as I've learned)... that's just random. so is she; but she's not the point, really.
the point is, every other place I've lived, I've put down roots and made friends. this is the exception. and it's not a good one. if you want to invite the world to live in your capital city, you have to get to know the people who take you up on your invitation.
and for the record -- this is the first time I've chosen a public forum to complain about it.
but for five years I've been reading umpteen articles moaning about how many americans there are running departments that the BBC (where my husband works), running the banks, etc.... it's silly.
if you don't like us, why don't you run your own companies? ...or at least, get to know us? ...for instance, at nursery. we've made a commitment to this country. that deserves minimal acknowledgment.
those of us with children have made a huge commitment to this country. to spurn that, is truly ugly. that's my opinion.
and for a point of comparison, it takes immigrants to the U.S. about five nanoseconds to assimilate into a culture that is prepared to welcome anyone with goodwill who works hard. ...we even make them Supreme Court Justices. and Presidents. .... for what it's worth.
I never thought it meant anything ,because people are different and just to judge them simply by nationality is one way of doing things and too over-simplistic for my taste. 
