Around a thousand far-right protesters shouting "Muslim killers, off our streets" marched through central London on Monday against a backdrop of swelling anti-Muslim feeling following the killing of a British soldier last week.
Lee Rigby, a 25-year-old soldier, was hacked to death in broad daylight in a south London street by two men who said they killed him in the name of Islam. The attack has shocked Britain and stirred an anti-Muslim backlash, including attacks on mosques.
In a tense but largely peaceful demonstration, supporters of the far-right English Defence League (EDL) rallied in London outside Prime Minister David Cameron's residence waving placards and shouting anti-Islamic obscenities.
"Islamic extremism is probably the number one threat to Britain," said one protester, Ben Gates. Other demonstrators chanted "Muslim bombers off our streets".
Another protester, Samuel Hames, said, of Rigby: "He survived his tour of foreign lands and comes home to his family and what happened to him is disgusting."
Nearly 2,000 people marched at a similar demonstration in the northern city of Newcastle on Saturday. Two men were arrested overnight for throwing firebombs at an Islamic cultural center in Grimsby, in the northeast of England. Similar attacks were recorded last week.
As anti-racist groups warned there could be more reprisals, Cameron came under intense pressure on Monday for going on holiday, with pictures of him relaxing in Ibiza prompting newspapers to question his leadership at a time of unease.
"Is Ibiza chillaxed (relaxed) enough for you, Prime Minister?" asked the right-wing Daily Mail newspaper.
Faith Matters, a charity working to defuse religious tensions, said it had registered a spike in reports of Islamophobic attacks in calls to its hotline, describing incidents as "very focused, very aggressive attacks".
Two war memorials in London were vandalized with red graffiti overnight, including the word 'Islam' spray-painted onto one monument.
Suspects Michael Adebolajo, 28, and Michael Adebowale, 22, allegedly ran over Rigby with a car near his army barracks and butchered him with knives. Police shot the two, and they remain under armed guard in separate London hospitals.
In a dramatic video clip shot by an onlooker and shown on British television, one of the two men, his hands bloodied, says he killed the soldier in retaliation for the deaths of Muslims killed by British troops in faraway lands.
Police have arrested 10 people in connection with the murder. Three people have been released on bail.
The attack prompted an emotional outpouring of sympathy in Britain, with well-wishers laying hundreds of flowers in the street where Rigby was killed. But some were openly angry.
"We've had enough of our soldiers being abused... We'd had enough of the plots and the violence," EDL wrote on its website.
In an attempt to counter the right-wing rally, anti-fascist group Unite Against Racism held its own demonstration nearby but was heavily outnumbered by EDL protesters.
A handful of far-right demonstrators threw bottles and coins at the anti-fascist rally. Police vans and officers blocked the two groups from approaching each other.
"They are a minority and a very scary growing minority," an anti-EDL protester who gave her name as Clara said. "I feel ashamed to be a Londoner today. This is disgusting."