The home secretary is planning to proscribe the Palestine Action group, effectively branding them as a terrorist organisation, Sky News understands.
Yvette Cooper is preparing a written ministerial statement which would make becoming a member of the group illegal.
The statement is expected on Monday and will then need to be enacted through new legislation.
It comes after pro-Palestinian activists targeted RAF Brize Norton and damaged two military aircraft – with Sir Keir Starmer describing their actions as “disgraceful”.
A security review has now been launched after the breach.
Brize Norton, in Oxfordshire, is the largest RAF station with approximately 5,800 service personnel, 300 civilian staff and 1,200 contractors.
In a video shared by Palestine Action on Friday morning, a person can be seen approaching an aircraft on a scooter as music is played. Red paint can be seen on the ground.
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The organisation – which focuses its campaigns on multinational arms dealers and has previously targeted corporate banks – said it had damaged two military planes at the base, where flights depart on a daily basis for RAF Akrotiri in Cyprus.
The group said two activists “broke into the largest air force base in Britain and used electric scooters to swiftly manoeuvre towards the planes”.
They said they did so because “despite publicly condemning the Israeli Government, Britain continues to send military cargo, fly spy planes over Gaza and refuel US/Israeli fighter jets”.
“Britain isn’t just complicit, it’s an active participant in the Gaza genocide and war crimes across the Middle East,” the group said in a statement.
“By decommissioning two military planes, Palestine Action have directly intervened in the genocide and prevented crimes against the Palestinian people.”
However a senior RAF source told Sky News’s Security and Defence Editor Deborah Haynes that the aircraft have nothing to do with Israel’s war in Gaza.
Sky News has contacted Palestine Action for further comment.
The two Voyagers – out of a fleet of 10 currently being used by the RAF – have been impounded while an investigation into the extent of the damage is carried out.
On X, the prime minister condemned the “act of vandalism”, adding: “Our Armed Forces represent the very best of Britain and put their lives on the line for us every day. It is our responsibility to support those who defend us.”
The Ministry of Defence (MoD) confirmed it is “working closely with the police, who are investigating”.
A “proscribed organisation” is an organisation or group that is illegal to join or show support for, because it has been identified as being concerned in terrorism.
The home secretary has the powers to proscribe an organisation under the Terrorism Act 2000, if that organisation commits or participates in acts of terrorism, prepares for terrorism, promotes or encourages terrorism (including the unlawful glorification of terrorism); or is otherwise concerned in terrorism.
