media captionLondon protests: Demonstrations move through the city
Thousands of demonstrators are marching through London in a day of protests.
Anti-lockdown and climate change demonstrations are under way across Westminster, Lambeth and Southwark alongside some smaller protests.
The Metropolitan Police arrested 12 people in raids in three areas of the capital on Friday and confiscated items linked to the protests.
The arrests were "proactive action" to reduce the likelihood of criminal activity, the force added.
Officers seized bamboo structures, lock-on equipment and other items.
Those arrested have been taken into police custody as inquiries continue.
image copyrightPA Mediaimage captionAnti-lockdown stickers were stuck to emergency service vehicles in Hyde Park
Thousands of protesters were seen marching through the streets of central London on Saturday.
Demonstrators packed the streets outside Downing Street.
Flares were set off while crowds shouted "shame on you" followed by prolonged booing.
Some protesters were seen throwing tennis balls at the Houses of Parliament.
One protester, who did not wish to be named, said: "They have little messages on them. Most of them are not very nice."
image copyrightPA Mediaimage captionSome protesters let off flares outside Downing Street during an anti-lockdown demonstrationAt the scene: Frankie McCamley, BBC News correspondent image copyrightGetty Imagesimage captionGatherings and marches are taking place in Westminster, Lambeth and Southwark on both Saturday and Sunday
Whether it was austerity or Palestine, lockdown or the NHS, campaigners of all ages and backgrounds wanted to make their voices heard today.
The pandemic put a stop to protests, but today campaigners came out in force.
It didn't matter your cause, all groups mixed and chanted alongside each other.
Thousands came to Regent Street bringing placards, flags and familiar chants.
Police closed off the roads allowing marches to pass through the capital, but some vehicles were stopped in their tracks.
Officers made their presence known but stood back allowing events to take place.
Climate protesters Extinction Rebellion said one of the raids took place at the Antepavilion centre – an arts and architecture charity.
Extinction Rebellion said an art installation of several bamboo structures, used in the group's blockade of the Broxbourne printworks in September, was confiscated.
The structures were on display after winning an Antepavilion award.
A spokeswoman said: "As far as we are aware, those arrested have no connection to the protest last September or to Extinction Rebellion."
Four more members were arrested at the Extinction Rebellion arts factory, the campaign group added.
image copyrightGetty Imagesimage captionAnti-vaccine and anti-lockdown protesters are marching through central London
Extinction Rebellion held a Kill the Bill demonstration alongside the anti-lockdown march.
The protest was prompted by the Police, Crime, Sentencing and Courts Bill, which proposes to give police in England and Wales more power to impose conditions on non-violent protests, including those that are deemed too noisy or a nuisance.
Ch Insp Joe Stokoe said: "Our policing plan will be proportionate with officers engaging with those protesting to help them ensure any gathering is lawful, safe and doesn't cause serious disruption.
"We urge anyone coming to take part in a protest in London over the weekend to do so in a peaceful and responsible manner.
"We believe certain protest groups are specifically intending to disrupt some business locations or potentially cause criminal damage to property.
"If this happens we will take further action as required to prevent offences being committed or deal with anyone committing criminal acts."