The United Kingdom banned Palestine Action under anti-terrorism legislation in July after some of its members broke into a Royal Air Force base and damaged military planes.
The group accuses the UK government of complicity in what it says are Israeli war crimes in the Gaza Strip.
Police have arrested hundreds of Palestine Action supporters in recent weeks under anti-terrorism legislation, including more than 500 in just one day last month, many of them over the age of 60.
On Saturday, hundreds of demonstrators gathered near parliament in central London to protest against the ban, with many holding up signs that said: "I oppose genocide. I support Palestine Action."
London's Metropolitan Police said about 150 people had been detained for a number of offences including assaulting police officers and supporting a proscribed organisation.
"Officers ... have been subjected to an exceptional level of abuse including punches, kicks, spitting and objects being thrown, in addition to verbal abuse," police said in a post on X
Mike Higgins, 62, who is blind and uses a wheelchair, was arrested last month but returned to demonstrate on Saturday.
"And I'm a terrorist? That's the joke of it," he said.
"I've already been arrested under the Terrorism Act and I suspect I will be today.
"Of course I'll keep coming back. What choice do I have?"
Palestine Action's ban, or proscription, puts the group alongside al-Qaeda and Islamic State and makes it a crime to support or belong to the organisation, punishable by up to 14 years in prison.
Police had warned ahead of Saturday's demonstration that anyone showing support for the group would be arrested.
Human rights groups have criticised the UK's decision to ban the group as disproportionate and say it limits the freedom of expression of peaceful protesters.
Palestine Action is challenging the ban in court, saying it is a peaceful protest organisation.
The government has accused Palestine Action of causing millions of pounds worth of criminal damage and says the ban does not prevent other pro-Palestinian protests.
Protesters also gathered on Saturday for a separate demonstration in London's Russell Square organised by the "Palestine Coalition" - which includes the groups Palestine Solidarity Campaign and Stop the War - while rallies took place in Belfast and Edinburgh as well.
with AP and PA
