"any more thoughts on the over-representation, or explanations for it?"

It's a difficult question, not one I'm qualified to 'explain'. Clearly British Pakistani criminal gangs are not over-represented in human trafficking per se, nor are they over-represented in the grooming of minors for sexual exploitation, but what they do seem to have successfully cornered the market in, is the highly public method of "on-street" grooming.

What interests me more than "why?" is "how?"

As I put it earlier, while white paedophile networks work covertly here, it is unlikely to be through choice rather than necessity. By contrast however, Western paedophiles are able to operate more publicly in places like Thailand where they are less likely to be confronted by the authorities. Similarly paedophile Catholic Priests were free to abuse minors for many decades in Catholic countries like Ireland, where they were also unlikely to be challenged by (secular) authorities.

What are the factors which enable particular individuals and groups to pursue their organised campaigns of abuse in full view (or at best lightly veiled), and in such a fashion that despite the fact that it is 'common knowledge' to the communities in which it occurs, the authorities fail to take appropriate action to end it?