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 and, according to police, included groups from across the UK linked to football disorder.
London's public transport network is also extremely busy.
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 will be 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, is in Whitehall.
Conditions have been imposed on both protests to ensure they remain in specific areas and 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, is also taking 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 they were intending to occupy roads and bridges.
Cdr Louise Puddefoot said: "[Youth Demand] has made no secret of their intentions.
"They have indicated that they will go beyond what can be considered lawful protest, instead trying to cause serious disruption to communities by blocking roads and the bridges that are essential for keeping traffic moving across London.
"We have seen in previous protests that when bridges are blocked, the impact on not just ordinary people but also ambulances and other emergency vehicles can be significant."
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's post added a number of people had been detained and details would be released later.
She added that the group had not informed the police of its plans to protest.
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.
If protesters do gather they will be restricted to a static demonstration that will be required to take place at a location away from sites that will cause obvious 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 Puddefoot added.
A four-day football family festival is also continuing in parts of the capital throughout the weekend.
Disruption is also expected on public transport due to the Champions League final.
While kick off is not until 20:00, Transport for London (TfL) said the Jubilee and Metropolitan lines are likely to be especially busy during the day with potential temporary station closures.
Stations including Baker Street, Bond Street, Canary Wharf, Charing Cross, Embankment, Marble Arch, Waterloo, Westminster, Wembley Park and Wembley Central are expected to be particularly busy, according to TfL.
The transport body said short-term safety measures could come into force at some stations, such as queuing, temporary closures, trains non-stopping and changes to entry and exits.
People with tickets for the final have been advised to leave plenty of time to get to Wembley Stadium.
The football festival 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.
Amid the multiple events taking place in London were rehearsals for Trooping the Colour on 15 June, for the King's official birthday.
Meanwhile, engineering work over the weekend means there are no direct train services between central London and Luton Airport, as well as no Elizabeth line services between Paddington and Abbey Wood.
Elizabeth line trains will also not run between Whitechapel and Stratford on Saturday.
TfL said people should check their journey on its website for updates before they travel.
