The Metropolitan Police said 42 people had been arrested in London by late Saturday afternoon.
All but one of the arrests were for showing support for a proscribed organisation, which police have said includes chanting, wearing clothing or displaying articles such as flags, signs or logos. Another person was arrested for common assault.
A further 16 arrests were made in Manchester, according to Greater Manchester Police, while South Wales Police said 13 people were also held in Cardiff.
In London, it was the second straight week protesters gathered to support the pro-Palestinian activist group.
Its outlawing has meant support for the organisation is deemed a criminal offence. Police arrested 29 people at a similar protest last weekend.
Two groups gathered underneath both the statues of Indian independence leader Mahatma Gandhi and South Africa's first post-apartheid president, Nelson Mandela, in Parliament Square.
Signs with the wording "I oppose genocide, I support Palestine Action", were held aloft in silence as the protesters were surrounded by police officers and members of the media.
Some demonstrators could be seen lying on top of each other on the ground as police searched their bags and took away signs.
Officers could then be seen carrying away a number of protesters who were lying down, lifting them off the ground and into waiting police vans parked around the square.
The official designation earlier this month of Palestine Action as a proscribed group under the Terrorism Act 2000 means that membership in the group and support for its actions are punishable by up to 14 years in prison.
Some 81 organisations are already proscribed under the UK act, including the militant groups Hamas and al-Qaida.
The government moved to ban Palestine Action after activists broke into a Royal Air Force base in Brize Norton in Oxfordshire, England, on June 20, damaging two planes using red paint and crowbars in protest at the British government's ongoing military support for Israel in its war in Gaza.
Police said that the incident caused around STG7 million ($A14.3 million) of damage.
Four people between 22 and 35 were charged with conspiracy to commit criminal damage and conspiracy to enter a prohibited place for purposes prejudicial to the interests of the UK.
The four are scheduled to appear on July 18 at the Central Criminal Court in London.
