The beating of Mr Denny was a long delayed reaction to another brutal beating, in March 1991, also caught on video-tape: that of a black motorist, Rodney King, by four white police officers.

ECONOMIST: Trouble in paradise

Briefing journalists ahead of his speech, the most senior Liberal Democrat councillor in Wales, Rodney Berman was clear that the white-hot anger which was felt on many doorsteps against his party since that deal between David Cameron and Nick Clegg in 2010 has begun to cool.

BBC: How much anger on the doorstep?

The Los Angeles Police Department itself was forced to change in the wake of the Rodney King case, which highlighted widespread racism in the largely white, male force.

BBC: Los Angeles riots figure Rodney King found dead