About three days ago, the police were involved in an operation involving an alleged armed drug dealer, during an intervention the suspect shot at the police and the police fired back, killing him.
All deaths-by-police are handled by the IPCC and the police organisations cannot make any statements about it until the investigation is complete. The family of the killed man held a protest outside their police station and it turned into a riot of sorts when the police wouldn't give them a statement (not that they had to, or were even allowed, because of the ongoing IPCC investigation).
It then kinda grew from there, except the riots and stuff going on is not a protest against anything, or any kind of dissent, it's just lawlessness: looters et al. just taking advantage of the situation.
Early calls that these were poor, disaffected youth were shot down after it was shown how these lootings are being organised on Twitter and people using BlackBerry Messaging. RIM has promised to reveal details of relevant BBM messages to the police.
(I find it amusing how RIM promotes their service as encrypted and secure to the public, when the public actually use RIM's public BBM servers which are not encrypted or protected from snooping eyes in any way).