Hey, Steve. I'm a longtime reader and I'd thought I'd throw out some interesting data. The government has estimated that 46 percent of the arrested rioters were black, 42 percent were white, and 7 percent were "Asian" (ie Indian/Pakistani/Muslim).
Using the census data on the ethnic makeup of the impacted riot areas and weighting those areas by the number arrested, blacks seem to have been arrested at 6-6.5x the white rate. Asians were arrested at about 0.85x the white rate. One downside to using the government data, with respect to Asians, is that it doesn't differentiate between Middle Easterners (Arabs, Persians, Afghans, Turks) and South Asians (Indians, Pakistanis, Bangladeshis, Sri Lankan Tamils).
I found a separate list of the names of the arrested rioters.
Looking through the names, I found that slightly under half of the Asian rioters were of Middle Easterners of non-South Asian origin (Morrocan, Egyptian, Arab, Persian, Turk). That's quite an overrepresentation when you consider that their numbers aren't especially large in the UK. Adjusting for their representation in the local population and making some reasonable estimates, it seems they were arrested at about 6x the white rate. This is a conservative estimate and the actual representation could be even higher.
For South Asians, I calculated estimates for three groups - Indian Hindus, Indian Sikhs, and South Asian Muslims (mainly Pakistani, some Bangladeshi, few Indian). Indian Hindus were arrested at 1/7th the white rate, Indian Sikhs were arrested at 1/2 the white rate, and South Asian Muslims were arrested at 0.8x the white rate.
Another source claims that the top nationalities of arrested rioters were Jamaicans, Somalis, and Poles.
None of these numbers are adjusted for age. The average rioter was 22 years of age and ethnic minorities tend to be younger than white British, so factor that in when looking at arrest rates.