Read more: http://www.dailymail.co.uk/news/article-1370053/Anti-cuts-demo-Protesters-occupy-Fortnum--Mason-half-million-march-London.html#ixzz1HkgLzsvu
Although above article makes the event look insane - check out following article which seems to show a more balanced view:
"Violence flared away from the rally when a group of hundreds of activists, not connected with the union protest, clashed with police. They set off fireworks, threw paint and attacked shops in Oxford Street, Regent Street and Piccadilly."
Read more here at "Independent"