Eight police officers were injured after clashes with hundreds of anti-establishment protesters in Parliament Square on the evening of the bonfire.
Protesters wearing Guy Fawkes-style masks had gathered in nearby Trafalgar Square for the annual Million Mask March, with fireworks launched at officers.
Images posted on Twitter showed protesters in Parliament Square where they were repelled by a line of officers wearing protective gear.
An effigy of Boris Johnson was burned as many protesters attending the event held signs protesting the coronavirus lockdown.
Metropolitan Police said 12 arrests had been made. He wrote on Twitter: “A total of 12 arrests were made during tonight’s police protests in London. These arrests related to various offenses. Eight of our officers were injured. This is unacceptable.
“The police operation will continue until the evening. “
The Met earlier said a Section 35 dispersal order was in place for “a number of areas” across Westminster, including Parliament Square. The force said: “The officers are engaging with those in Parliament Square and will inform them of this order. “
In another tweet, the Met said a crowd in Parliament Square “dangerously started fireworks and rockets.”
He added: “Some hit people or exploded near the crowd, it could cause very serious injuries. We moved through the crowd to remove all fireworks and keep people out [from] come to evil.
One participant, who only gave his name to Richard, from London, said the protest, which has taken place on November 5 for several years, was a “continuation” of “anti-Covid” marches.
“It is essentially a continuation of the anti-Covid marches that we have been leading since the start of the year,” he said. “It’s a few fingers in the direction of the establishment. “
Ahead of the protest, the Met said officers would work closely with protest groups to “ensure gatherings are safe and disorder is minimized.”
Last year, nearly 200 people were arrested during the protest for violating lockdown restrictions.