Not sure yet but I think these are ‘anti-war’ protesters.
Below is the description from the video:
Protesters break into bank, clash with cops as London march turns violent
Follow latest updates at http://twitter.com/rt_com and http://www.facebook.com/RTnews Tens of thousands of mostly peaceful demonstrators streamed into central London on Saturday to march against government budget cuts, with a small breakaway group smashing its way into a bank, breaking windows and spray painting logos on the walls. Another group of black-clad protesters hurled paint bombs and ammonia-filled light bulbs at police. Organisers of the march estimated that at least 250,000 people from across the country were peacefully joining in the demonstration, the biggest protest in London since a series of rallies against the Iraq war in 2003. Police said they were not giving out crowd estimates.