I am aware of the different backgrounds of British Pakistanis compared to American Pakistanis, and how the former have struggled a lot more, but I don't agree with is why that should contribute to British Pakistanis being less well-integrated compared to their American counterparts?
OK, let me try and explain.
As mentioned previously, the Pakistanis came to work as manual labourers in the cotton & woollen mills of the North and the heavy industries of the Midlands. So just like most newly arrived, uneducated immigrants, they performed the worst and lowest paid jobs. To make matters worse, apart from feeding and looking after themselves, they also needed to send the little money they had back to support their families back home.
Result? They congregated together, living in the cheapest and most deprived parts of the twon and cities. As newcomers came, they too gravitated towards the same areas. Then they brought their families to live with them - again in the same areas. They formed ghettos.
When the factories closed en mass and caused massive unemployment, those living in these ghettos were the worst off - for all the reasons explained earlier.
But, those that did manage to improve their lot, acquire decent education / good jobs / acquire a little bit of wealth, they started to move out and disperse into the more upmarket suburbs, with better schooling, better facilities, lower unemployment etc.
You will find that these British Pakistanis, by and large, are just as integrated as their American counterparts (- having lived/worked in the States for a few years, and now living in one such area, I can verify this personally).
As for the American Pakistanis, coming from middle class/ wealthier / educated backgrounds (as students, doctors, engineers etc), their starting point in the States was very similar to those British Pakistanis who had managed to move out of the deprived inner city areas.
Not only that, but they had no need to send money back to support their wealthy middle class families back home. meaning that they could afford better housing, live in better areas with better schooling etc. You get the picture.
If anything, they should be more thankful that they have managed to better their lives and that of their future generations by moving to the UK, which should motivate them to assimilate better.
It's not easy as you may think. Living in a deprived area means worst schools, fewer jobs, higher crime rates - and even organisations like Banks and Insurance companies (say for insuring your car - which is compulsory in the UK otherwise you can't drive the car on a public road) work against you by increasing their rates and/or denying you loans and refusing to insure you.
Let me give you an example of a current situation which does not even involve someone living in a deprived area.
Because of the large discrepency of house prices in the UK between London & the South east versus the North, if a family man living in the North, with a good job and a decent house in a good neighbourhood, is made redundant but is offered a new job in London / the South-East (even with a larger salary), he will most likely turn it down.
Why? You may ask.
The reason being that the price he will obtain for selling his big family house in the North, will unlikely be enough for a flat/house half the size in a deprived area of London ie Not large enough for him and his family to live in. Thus he's stuck in the North unless he can get a mega increase in his salary for relocating which will enable him to take on a much larger mortgage for a larger house in a decent area of London.
Now translate that to someone low paid or unemployed living in a deprived inner city area of a Northern town trying to move to the suburbs with better housing, better facilities, better schools, better prospects for employment. Basically, he's stuck in his ghetto, that of the British Pakistani community containing none other than British Pakistanis, with all the aforementioned probems. And so the circle continues for his children. (That's not to say that every now and then some, like my parents, manage to break out of that circle and move to better areas where 'they can integrate')
they are everything they hate.
