Yvette Cooper has defended the arrest of more than 500 people for holding signs supporting Palestine Action.
The home secretary said protesters over the weekend may have been objecting to the group being proscribed as a terror group because they “don’t know the full nature of this organisation”.
Ms Cooper said that could be due to reporting restrictions on court hearings “while serious prosecutions are underway”.
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A total of 532 people were arrested on suspicion of supporting a proscribed organisation contrary to Section 13 of the Terrorism Act 2000.
Around half of them (259) were aged 60 and above – including almost 100 people who were in their 70s.
The Met Police said it was the largest number of arrests it had made related to a single operation in at least the past decade.
Ms Cooper added: “Proscription is not about protest around Palestine or Gaza, where we had tens of thousands of people protesting lawfully just this weekend about some of the horrendous events that we’ve seen in the Middle East.”
She said members of Palestine Action have carried out violent attacks causing injuries and involving weapons and smoke bombs “causing panic among innocent people” and major criminal damage against national security infrastructure.
The home secretary added there had been “clear security assessments and advice” before Palestine Action was proscribed as a terror organisation in July.
Former government lawyer Tim Crosland, now spokesman for Defend Our Juries, which organised the weekend’s protest, told Sky News: “Yvette Cooper is so politically invested she’s going to continue to defend the arrests of people simply protesting.
“There will be more people at the next action, the police will be so aggrieved that they’re having to arrest people holding placards protesting against the atrocities in Gaza while they’re having budget cuts.”
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Sir Keir Starmer’s spokesman said the group was proscribed based on “strong security advice” following assessments from a “wide range” of experts across government, the police and security services.
“Those assessments were very clear this is not a non-violent organisation,” he said.
He added Palestine Action had committed “three separate acts of terrorism” but could not go into further detail as further evidence had been provided in a closed court setting due to “ongoing national security reasons”.
Human rights group Amnesty International said it was “deeply concerned” about the arrests this weekend.
Its UK chief executive, Sacha Deshmukh, said: “The protesters in Parliament Square were not inciting violence and it is entirely disproportionate to the point of absurdity to be treating them as terrorists.
“Instead of criminalising peaceful demonstrators, the government should be focusing on taking immediate and unequivocal action to put a stop to Israel’s genocide and ending any risk of UK complicity in it.”
