One man has been stabbed after a group of "neo-Nazi Polish fascists" attacked a free music event in Tottenham, north London.
Officers were called following reports of a disturbance at Markfield Recreation Ground on 21 June in which a free community music festival was taking place.
Footage has emerged of the disorder which occurred during the "unprovoked attack", which saw rocks and fireworks being hurled.
A 24-year-old Polish man was stabbed during the incident. He was taken by London Ambulance Service to an east London hospital where his condition is not believed to be serious.
Members of the local Orthodox Jewish community were also targeted by the mob.
One man has also been arrested on suspicion of racially and religiously aggravated common assault, after he allegedly pulled a kippah (skull cap) from a man's head.
No one has been arrested in connection with the stabbing.
According to Oz Katerji, a journalist who witnessed the attack: "About 150 of us were having a party in Markfield Park in Tottenham, neo-Nazi Polish fascists turn up, full scale riot erupted."
Haringey Green Party has said those responsible for the attack are a Polish fascist group known as the Zjednoczeni Emigranci, who are alleged to have ties to hooliganism in Poland.
A Green Party spokesperson said: "On Saturday 21st of June, there was a licensed community event in Markfield Park, South Tottenham. Unknown to the locals, police, and anti-fascist campaigners, a small extreme nationalist Polish group, Zjednoczeni Emigranci (literally translated as United Immigrants) had also planned an event nearby.
"Taking the peaceful community event by surprise, ZE launched an unprovoked attack, hurling verbal abuse at locals, intimidating the children and families that were present, before turning to physical violence."
In a response to the attack, anti-fascist group Unite Against Fascism (UAF) organised a vigil opposite Tottenham's Town Hall on the evening of 23 June in order to "stand united as a community".
A Met Police spokesperson said: "A group of around 20 people, predominantly male and from the Eastern European community, arrived at the location during the course of the event. This was a loose collection of people - not a designated march.
"Enquiries continue into the subsequent disorder, during which fireworks were thrown. We are not aware of any further injuries.
"A 22-year-old Polish man was arrested after a man's kippah was pushed from his head. He has subsequently been charged with racially and religiously aggravated common assault."