More than 2,000 officers are on duty in London to police the Champions League final, a protest organised by the far-right activist Tommy Robinson, and a counter-demo.
Thousands of people attended the march and rally in Parliament Square organised by Robinson, whose real name is Stephen Yaxley Lennon. According to police they included groups from across the UK linked to football disorder.
London’s public transport network is also extremely busy, with part-closures and severe delays adding to congestion.
Borussia Dortmund will take on 14-time champions Real Madrid at Wembley Stadium on Saturday evening.
Robinson’s protest set off from Victoria and ended in Parliament Square where speeches were given and a film was shown.
On X, formerly Twitter, the Met said: “Officers are aware of a number of groups that have gathered in pubs nearby and elsewhere in central London.
“They include people known to the police for football violence. Officers are closely monitoring these groups.”
A static counter-protest, organised by Stand Up To Racism, took place in Whitehall but has since ended.
The Met said officers would be deployed “in significant numbers” to ensure those in Parliament Square and Whitehall do not come together.
Around 400 of the officers are from police forces outside London.
A third demo, smaller in size and unrelated to the above events, also took place in central London.
Youth Demand said it wanted to take direct action in protest against the ongoing conflict in Gaza, and said in public statements its members were intending to occupy roads and bridges.
The Met posted on X that protesters “went onto York Road, attempting to cause serious disruption by blocking traffic” despite being “subject to conditions not to leave the pavement”.
The force later posted that nine people had been detained for “breaching Public Order Act conditions not to leave the pavement”, adding “the remainder of the group has largely dispersed”.
Officers have also tried to curb a planned demo against the conflict in Gaza in the Finchley area by imposing restrictions under the Public Order Act.
The Met said if protesters do gather they will be restricted to a static demonstration to take place at a location away from sites that may cause fear and concern to Jewish residents, but that is still of importance to the protest organisers.
“There is a significant difference between a protest that takes place in central London on a Saturday away from residential areas, and a protest that seeks to walk right through an area with a significant Jewish community. It is right that our policing response takes this into account,” Cdr Louise Puddefoot said.
A four-day family football festival is also continuing in parts of the capital throughout the weekend.
It has been taking place at several sites in central London, including Trafalgar Square, Regent Street, Somerset House, the South Bank and Potters Field Park, with road closures in place as well as changes to some bus routes and Cycleways.
It is due to finish on Sunday evening.