Protesters on both sides of the divide over the UK’s migration policies gathered outside a hotel in Canary Wharf, east London, on Sunday afternoon.
They included about 20 anti-migration demonstrators, some of whom wore masks and carried Union flags, and several children.
Across the road, around 100 counter-protesters held banners bearing the words “stand up to racism” and “stop the far right”.
The group chanted “say it loud and say it clear, refugees are welcome here” while people across the road shouted back “no, they’re not”.
Later, police said a group, including some wearing masks, moved into a Canary Wharf shopping centre where “a small number of masked protesters then became aggressive towards members of the public and police”.
The force said four arrests were made including for common assault by a protester on a member of the public, possession of class A and B drugs, assault on police, public order offences and failure to disperse.
One officer was punched in the face but did not suffer significant injury, police said.
The Met said officers had used Pava spray, a synthetic form of pepper spray, after they had “witnessed an assault by a protester on a member of the public” in the shopping centre.
The force added: “The suspect was immediately arrested by officers who used Pava spray.
“We are aware other protesters and members of the public, including a child, may have been temporarily affected by the use of Pava given the density of the crowds in the area.”
A Section 60AA order, giving officers the power to order the removal of face coverings for the the Isle of Dogs area south of the A1261, has been put in place as well as a dispersal order.
Both orders last until midnight, police said on Sunday evening.
Commander Adam Slonecki, in charge of policing London this weekend, said: “We had plenty of officers on the ground who moved in swiftly to deal with the criminality that occurred inside and outside the shopping centre.
“We will not tolerate this kind of behaviour.
“Today’s protest saw many community members attend, including women and children, and we worked to ensure the safety of those there to peacefully represent their views.
“Those who arrive at protests masked and intent on causing trouble will continue to be dealt with robustly at future protests.
“We remain in the area to deter any further disorder and provide reassurance to local residents and businesses.”
Migration protests have been held across the country over the weekend after the Government won a court challenge on Friday, meaning asylum seekers can continue to be housed at the Bell Hotel in Epping, Essex.
