The neon-clad bobbies (cops) with their arms held behind their backs as they stood watch in the daylight hours became a common sight--as well as a fitting symbol. Like this man guarding the city centre post office, the cops essentially had their hands tied when the city needed them most.
British police typically carry no guns and were basically not permitted to interfere with the vandalism occurring the first night of the riots in Birmingham. Only if human life were threatened were they allowed to intervene. So, as in London--where the riots began--they most often could only watch as the destruction took place. Though they attempted to prevent and stop the rioters on the second night, it did little good (the riots grew worse and three people were murdered).
Only on the third night of riots in Brum were the police given the power to use rubber bullets. But, by then, the riots were over.