Can't comment on the UK, but I was involved with the first real prison race riot in Victoria, muslims against Islanders and there NZ cousions.

PC government refused to except it was race based, believing they can all live together happily.
There has always been prison gangs and fights [drug supply] being the prime goal. but these fights are normally prison wing fights, easily contained.

Race based riots are a different story then a normal riots, normal riots usually are about damage to prison property, when they finish burning etc it all calms down and you go in and take back control, softly, softly, very PC.

Race riots are a different kettle of fish, they are not only prison wide, but can erupt in multipule prisons at the same time.

If you have a ratio of 4 Officers to 100 prisoners and rioting over a large area of several prisons, you can't get the officer numbers to put a stop to it.

You tube Victorian prison riots, the Government refuses to except there is a problem.