For one thing, Crimewatch is a man-hunt show. Think that through. Who is more likely to go undetected? A life-long Brit man who has lived in the same town for 50 years, or a recent immigrant who has managed to lose himself amid a community of fellow immigrants?
And, by it's very nature, it majors on certain crimes and ignores others. Don't use it as a true reflection of UK crime statistics.
But still, I take your point. So here's mine:
You could equally draw a comparison between high crime and low income. In fact, the correlation would be glaring even if you took race entirely out of the equation. Just as it was in 1990 and 1890 and 1790. But I doubt you'd be interested in doing that, would you?
By your rationale, statisticially, one in ten paedophiles should be black as well. And yet I doubt whether they are. Being a bit selective about the evidence again?