Anti-capitalism protesters from the Occupy movement have begun a new protest in the City of London as part of a global day of action.
Other protests are underway in cities including Moscow, New York, Athens and Madrid.
Several hundred people have gathered outside St Paul's Cathedral for a rally, before moving on to demonstrate outside the offices of some of the largest firms in the financial heart of London.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.