Some 58 people have been arrested in London after BNP supporters and anti-fascist campaigners came to blows outside the Palace of Westminster.
Scotland Yard said those arrested were members of the United Against Facism protest, and were held for suspected public order offences.
The fighting came despite calls for peace from police and the family of soldier Lee Rigby, who was hacked to death in Woolwich last month in what police are treating as a terrorist attack.
The BNP had planned to march from Woolwich Barracks, but were banned from doing so by Scotland Yard, amid community fears that their presence could prompt disorder.
BNP leader Nick Griffin warned that the murder of soldier Lee Rigby would not be an isolated incident.
He said: “I believe that by being here today we have at least taken a step to taking the debate to where it needs to be.
“Not about whether the terrible murder of Lee Rigby was isolated, something which will never happen again.
“We’re pointing out that it will happen again and again and again until the West disengages with Islam and they leave our country.”
Meanwhile, rival protests by the Scottish Defence League (SDL) and anti-racism campaigners took place in Edinburgh's Old Town.