Hundreds of people are expected to risk being arrested as people gather to protest in support of Palestine Action - which was designated a terror group by the UK government.
Several people have already been arrested in Parliament Square as police were seen dragging some protestors away as they were detained. Other protestors were seen holding placards reading "I oppose genocide, I support Palestine Action" as many remained sat and silent on the green.
Other protestors are set to march for Palestine as they call for the UK government to stop selling arms to Israel, amid horror images of children being starved in Gaza.
The Metropolitan Police said it has drawn officers in from other forces to help form a "significant policing presence" in the capital as it faces a busy weekend of protests.
A seperate Pro-Palestine march, organised for today, has set off from Russell Square towards Downing Street.
The Metropolitan Police said one person has so far been arrested at the Palestine Coalition march "for a placard showing support for Palestine Action", the force said.
This march is due to pass through Aldwych and the Strand, before reaching Whitehall.
Defend Our Juries said between 600 and 700 people were participating in the protest supporting the banned Palestine Action in Parliament Square.
The group, who organised the demonstration, claimed the Metropolitan Police were preparing for "the largest mass arrest in their history" after expecting a turnout "in the low hundreds".
Metropolitan Police officers began arresting protesters in Parliament Square holding placards supporting Palestine Action.
Clusters of officers could be seen holding individual protesters sat on the edge of the grass and escorting them through swelling crowds to police vans on the edge of the square.
A separate group of officers could be seen attending to a protester lying next to the fenced-off Emmeline Pankhurst statue.
The main, larger group of protesters in the middle of the central London square remained sat quietly holding their placards.
A large group of protesters have gathered in central London to show support for the banned Palestine Action.
The crowd, sat on the grass inside Parliament Square, could be seen writing "I oppose genocide, I support Palestine Action" on white placards at 1pm, with the vast majority remaining silent.
Several demonstrators carrying placards that read "Palestine Action terrorises Britain while Hamas hides in hospitals, schools and mosques", briefly walked along the crowd before being led away by Metropolitan Police officers.
Other clusters of protesters who were not holding placards gathered around the Mahatma Gandhi and Nelson Mandela statues in the square singing pro-Palestinian chants.
Organisers Defend Our Juries previously said more than 500 people would be participating in the protest.
The Met Police said it brought in cops from other forces for today's protest.
The Met Police's Deputy Assistant Commissioner Ade Adelekan warned protestors showing support for Palestine Action could be arrested today.
Adelekan said: "Anyone showing support for Palestine Action can expect to be arrested. I would once again urge people to consider the seriousness of that outcome.
"An arrest under the Terrorism Act can have very real long-term implications – from travel, to employment, to finances. Also, as we have seen this week, it is very likely an arrest in these circumstances will lead to a charge."
A man is detained by police officers as supporters of Palestine Action take part in a mass action in Parliament Square, Westminster.
Several police officers were pictured detaining the man and walking him away from the gathering.
The Home Office has defended its decision to label Palestine Action a "terror group" saying the ban was "not about Palestine".
A Home Office spokesperson said: "The Home Secretary has been clear that the proscription of Palestine Action is not about Palestine, nor does it affect the freedom to protest on Palestinian rights.
"It only applies to the specific and narrow organisation whose activities do not reflect or represent the thousands of people across the country who continue to exercise their fundamental rights to protest on different issues.
"Freedom to protest is a cornerstone of our democracy and we protect it fiercely. The decision to proscribe was based on strong security advice and the unanimous recommendation by the expert cross-government proscription review group."
More than 500 people are expected to hold up placards supporting the group in Parliament Square, after organisers Defend Our Juries announced earlier this week the event would go ahead.
The ban means that membership of, or support for, Palestine Action is a criminal offence punishable by up to 14 years in prison, under the Terrorism Act 2000.
