The Metropolitan Police said that by 8am on Monday there had been 21 arrests in connection with the Extinction Rebellion protests.
The arrests are in addition to those over the weekend, with eight people arrested on Saturday – seven on suspicion of conspiracy to cause public nuisance, and the eighth on suspicion of obstructing police.
All those arrested on Saturday have been released under investigation.
And on Sunday one woman and two men were arrested on suspicion of conspiracy to cause public nuisance.
The woman has been released under investigation, the men remain in custody, the police said.
Extinction Rebellion protesters playing steel drums marched from Parliament Square to Trafalgar Square where they plan to kick off two weeks of disruption in the city.
A 25-year-old teacher from London who took the week off to join the protests said: “The plan is to shut down the whole of London.
“The issue of climate change is an issue for everyone, and it’s clear we can’t leave it to the politicians.
“I booked the week off work for this.
“The school kids are out protesting too. Everyone is.”
Police are searching anyone suspected of carrying paint.
Extinction Rebellion said protesters from the XR Peace group arrested as they blocked Victoria Embankment outside the Ministry of Defence included 81-year-old Sarah Lasenby, a Quaker and retired social worker from Oxford.
She said: “For 21 years my main concern has been to help get rid of UK nuclear weapons.
“I am still keen to do this but once I came across XR I was so relieved to have something I could do about the ghastly state we have got our planet in.”
And she said: “The whole thing is so urgent that it is imperative the Government should take serious actions and put pressure on other states and Global Powers to radically reduce the use of fossil fuels even if this means we need to reduce our comfort at home and so much flying.”
Protesters have been carried away by police officers on Guards Road.
An onlooker said he saw at least five people arrested after they refused to let a van through the road.
Video of the moment shows people being carried off to chants of “we love you” from other protesters.
REUTERS