An anonymous iSteve commenter has gone through a gallery of surveillance camera photos of rioters posted by the Birmingham, England police department and attempted to work out what the press hasn't been in a hurry to report. Granted, a lot of the pictures are pretty fuzzy, and most of the hoods are wearing hoods, but here are his estimates (feel free to go to the link and compile your own estimates):
Looking at those pics of rioters and toting them up in a spreadsheet - the demography is 60% Black, 35% White, 5% South Asian.
Demography of the city of Birmingham (where the shots are sourced from) is - " 70.4% of the population was White (including 3.22% Irish & 1.49% Other White), 19.5% British Asian, 6.1% Black or Black British, 0.52% Chinese, 2.9% of mixed race and 0.63% of other ethnic heritage."
So merging mixed race and Black, we have a per capita representation level of White - 0.5, Black (amalgamating Black and Mixed race in the American fashion) - 6.7 and South Asian - 0.25 (assuming they are all Pakistanis and Bangladeshis, those would have a rep of around 0.35).
Now since the demographics are younger around ethnic minorities and older among Whites, I'd say that it probably normalizes to age around 6-8x White representation level among Blacks and a 1/4x White representation level among South Asians (and you could take it as 1/2 White representation level among Muslims, if you assume they're all Muslims, and correspondingly assume 0 Hindu representation).
Of course, the totals as a whole might be Blacker or Whiter depending on how the other areas work out - I'd guess them to wash out at least somewhat Blacker and less White and South Asian, considering London is where the main action is at.
So, blacks 6-8X versus whites sounds about like the usual racial ratio in crime rates seen in America.
There's a lot of evidence that young white Brits commit more assaults and burglaries than young white Americans, but the ratios are not gigantically different.
Also, it seems like the white crime rate is much worse in Britain than in America because serious white youth crime has largely vanished from major cities in America, while it's concentrated in big cities in Britain. For example, in 2010, I looked through 2,600 homicides in Los Angeles County over a few recent years, and off the top of my head, I can recall seeing only one white-on-white youth homicide in a parking lot at night that didn't involve Armenians or other white immigrant groups. (That one was in exurban Stevenson Ranch). But, just because young white men in the biggest American cities tend to be middle class or higher these days, and stay well away from violent crime, doesn't mean that's true all across America.
We think of riots in the U.S. as being race riots and thus as being segregated, but that's probably not quite as true as it seems. For example, when my future wife in April 1968, after Martin Luther King was murdered, looked out her window on the ghettoizing west side of Chicago and said, "Look, Mom, free TVs! Let's get one!" a majority of the neighbors lugging TVs down the street were white. Same for the yuppies who looted coffeetable books of Impressionist paintings from Chicago's best book store on Michigan Avenue after the Bulls won in 1992.
In general, the term "race riot" can be misleading because there have been very few intercommunal mass riots in the U.S. in recent decades. We've had black v. middleman minority riots, as in blacks v. Koreans in L.A. Perhaps Crown Heights where blacks attacked Hasidim 20 years ago (and the Democratic candidate hasn't won any of the five mayoral elections in NYC since).
Something to keep in mind is that English riots tend to be less deadly than the worst American riots. The official death toll in South Central LA in 1992 was over 50, in Detroit in 1967 over 40 (and a reader whose father was an emergency room doctor in Detroit during the riot says his father told him the actual death toll was significantly higher), and in Watts in 1965 over 30. I presume that the large number of guns in America make a difference.
So, lots of American riots are, like these in London, "political shopping." But they tend to be more segregated because they are more dangerous, so whites who wouldn't mind playing smash and grab for a night or two tend to stay home because they don't want to risk getting shot by black rioters or by cops.