Theatregoers scurried out of the way as police and marchers fought in Trafalgar Square, the destination of more than 10,000 protesters, some of whom had earlier clashed with police outside the Foreign Office and the entrance to Downing Street, where more violence took place.
While a Reclaim the Streets party went on in the middle of the square, other demonstrators at the square's edges broke up paving stones and threw them at police, with manhole covers and scaffolding. The police replied with baton charges. A number of people were injured, with at least 10 arrests.
Officers were keen to avoid a repeat of the poll tax riot which got out of hand in the square under similar circumstances in 1990. Organisers had promised a "carnival atmosphere".