Around 1,000 EDL protesters then made their way along Whitehall before taking a position on the pavement across the road from Downing Street.
A smaller group of anti-fascist demonstrators gathered opposite them holding an "EDL Racists" banner.
Both sides traded insults but were kept apart by officers and barriers.
The EDL supporters chanted: "We hate Cameron."
The anti-fascist supporters chanted: "Racist scum off our streets."
More top news
William and Kate were forced to change some of their programme when forecast torrential rain swamped the rural settlement of Bella Bella.
The Hollywood actor popped over to say hello when he saw the happy couple posing for pictures in New York's Central Park.
Half of those killed or maimed in the last 72 hours of intense bombardments in Aleppo have been children.