Well, there are several factors affecting it, and both sides are to blame.
For our part, we trust the opinion of some bloke down the pub as to what is 'normal behaviour' for people from other countries, and very rarely actually ask
them. We jump to conclusions, something that is, oddly enough, actively encouraged by our government.
For their part, it's the whole 'acceptance/integration' thing. I certainly know some immigrants whose opinion of the English has been achieved in exactly the same way as our opinion of them. There is also the culture thing, if I were moving to France, when I arrive I'd be sure to learn about the culture and its etiquette. Anyone who's heard tales of retired British living in France, never bothering to learn the language or customs will see where the problem arises. It's not easy to change your entire life when you are over 30, and our government dithers a great deal out of what is expected of someone, regardless of origin, who lives in the UK.
Take queueing for example, it seems like a silly thing at first, the British form queues almost by instinct. It's considered 'rude' to jump queues. Some other countries don't do that, it's not because they are more 'rude' or anything, it's just not part of their society. The great British queue may seem like a tiny insignificant thing to give, but it's not, not because it's right or wrong or anything of the sort, but simply because it is part of our society. I was bought up being told that wearing a hat indoors was the height of bad manners. If I were told that in another country and still walked around indoors in a hat, I'd have it pointed out to me in no uncertain terms.
I'm not saying these social 'laws' are right or wrong, they are simply part of our culture, but nobody ever explains our culture properly to people moving here, and that is why they don't really understand it on occasion. They are left as Strangers in a Strange Land, and nobody seems inclined to tell them the rules, the laws, yes, but not the rules. For a coutry that always stresses to it's holidaymakers to learn and respect the customs of other countries before visiting them, I find that pretty odd.
As far as the amount of immigrants, as Aldo says, it's where they were put. The favourite was London, because immigrants= Income and as far as our government are concerned London will always come first. As far as immigrants 'living off the Social Services' are concerned, I can assure you, there are a lot more British doing exactly that, and have been for years than there are immigrants. You will always get people who live off the system, the answer to that lay not in the people, but in the system and it's rubber stamp method of dsealing with people.
Anyway, long post over

Edit : Let me put it this way, there'd be all hell to pay if I walked into a Mosque in Edmonton with my shoes on, and yet no-one says a word if I'm pushed out of the way in a Bus queue. That, to me, is just wrong, it's all a question of etiquette.