Around 1,500 people gathered outside the parliament on Saturday afternoon, according to the organizer.
People waved Palestinian flags, chanted "free Palestine" and carried signs with messages such as "I oppose genocide, I support Palestine Action", reports BBC.
The London police state that those arrested attacked police on site or expressed support for the banned group. According to a statement, the police have been subjected to "punches, kicks, spitting and thrown objects, in addition to verbal abuse".
The absolute majority of those detained were suspected of having shown support for the organization.
In parallel, a pro-Palestinian demonstration was taking place in London with around 20,000 participants. It is said to have been calm there, according to the police, who had deployed more than 2,500 police officers to handle the protests.
Supporters of Palestine Action have carried out a series of protests across the UK since the beginning of July, when the parliament banned the group with reference to terrorism legislation. This happened after activists broke into a British air force base and vandalized two tanker planes.
The measure means that it is prohibited to participate in the group and publicly express support for it.
