Keith is simply looking for an explanation of this phenomenon.

On the information and suggestions posted here, I favour Don's
"a case of criminal activity of a localised group of interacting gangs who are Pakistani because gangs tend to consist of just one ethnic group."

---
Just as I have been asking why are homosexuals so over represented in hiv/ aids figures?

If you are getting at what I think you are, I probably agree with you.

While I do think one needs to be extremely careful in (I suppose) presenting theories, I think there can be a danger in being politically correct to the point of ignoring or not daring to look at something that could be important. It's not easy...