So just to make it absolutely clear: according to these London figures black offenders should constitute approx 54 - 67% of the prison population (so between 5.4 and 6.7 times what would you expect based just on their population of 10.6%).

According to the figures you pulled out of the Guardian article, black people make up 3% of the population in England and Wales and 12% of the prison population'. That's 4 times higher.

IF you can extrapolate the rate of crime by race in London to England and Wales as a whole, then there should be MORE black people in prison than there actually are.