The Metropolitan Police have arrested 117 people on suspicion of showing support for the proscribed organisation Palestine Action.
It follows a protest outside the Royal Courts of Justice today.
Judges ruled that the ban on Palestine Action as a terror group was lawful.
Soon after the Court of Appeal's ruling, the Metropolitan Police confirmed that arrests were "underway" and reiterated that support for the group is a criminal offence.
Outside London's High Court, a gaggle of protesters brandished pro-Palestine Action placards, a number of whom have now been detained by officers.
Some of those supporting the proscribed organisation yelled "shame" and "you're complicit" at police officers.
They held signs reading "I support Palestine Action."
A Met Police spokesman said: “We acknowledge the Court of Appeal’s judgment that the Home Secretary’s decision to proscribe Palestine Action was lawful."
The Metropolitan Police have arrested 117 people on suspicion of showing support for a proscribed organisation following a protest outside the Royal Courts of Justice
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They added: "This means that expressing support for the organisation remains a criminal offence and officers will arrest those who break the law.
"Officers policing a protest outside the Royal Courts of Justice today, Monday, June 15, arrested 117 people on suspicion of expressing support for a proscribed organisation.
"A further two people were arrested by colleagues in the City of London Police at a protest outside the Old Bailey.
"Since the organisation was proscribed, the Met has arrested over 3,000 people on suspicion of expressing support for Palestine Action."
Protesters held signs reading 'I support Palestine Action'
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Earlier this year, three judges claimed the decision to proscribe the group was "unlawful" and Yvette Cooper's ban on the organisation should be reversed.
The legal challenge was brought before the court by the organisation's co-founder, Huda Ammori.
The ban, which came into force on July 5, made membership of or support for the organisation a criminal offence, punishable by up to 14 years in prison.
It has remained in place while the Home Office battled the legal challenge launched in February.
Protest broke out outside the Royal Courts of Justice today
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Shabana Mahmood's department argued that criminal sanctions against the activists were "insufficient" after the group ramped up its protest efforts.
Earlier today, five of Britain's top judges sided with the Government and ruled that the decision to ban the group was lawful.
Lady Chief Justice Baroness Carr said that any comparisons to historical groups, such as the suffragettes, were "seriously flawed".
She added that the High Court had "materially understated the position" when considering how much latitude the Home Secretary had when making the decision last July.
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