James, i'm not sure that's what's happeningen in Londen
Haha, it's a song about the London riots I believe. In 2011 there were wide-spread riots across the UK, the vast majority of it in London. Police were outnumbered, many called in from other parts of the UK, buildings burned down, stores robbed ect. Loads of people went nuts over the police shooting some criminal because they thought he was reaching for a gun. The thing is, the police were totally correct in doing so, and we have tiny numbers of people killed by police in the UK.
The song is basically going "Let's all not be asshats and be good people". It's about a bunch of people dressed as gangsters who look like they're about to start shit who go around doing good deeds. At least, that's my interpretation of it.
CCTV footage of the guy's bag being opened: Common scene in the media where a kid was robbed
Riot police at the end, outnumbered vs protesters
BBM (the messenger used at the start) played a big part in the rioters organisation, and it says "RIOT"
Those are some reasons I think that's what it's about.