The group Palestine Action said two members entered RAF Brize Norton on Wednesday and used electric scooters to approach the Voyager jets, which are used for air-to-air refuelling and transportation.
The duo sprayed red paint into the planes' turbine engines with repurposed fire extinguishers and caused further damage with crowbars, according to the group, which released video footage appearing to show an individual approach a jet and spray paint into the engine.
The activists left the base without being detained, Palestine Action said.
The group said that "despite publicly condemning the Israeli government, Britain continues to send military cargo, fly spy planes over Gaza and refuel US/Israeli fighter jets".
It called the UK "an active participant in the Gaza genocide and war crimes across the Middle East".
Prime Minister Keir Starmer condemned the "vandalism" as "disgraceful" in a post on X.
Britain's defence ministry confirmed the incident, saying: "We strongly condemn this vandalism of Royal Air Force assets."
Planes from Brize Norton, about 100km northwest of London, regularly fly to RAF Akrotiri in Cyprus, Britain's main air base for operations in the Middle East.
The UK has sent more Typhoon fighter jets and Voyager tankers to Cyprus since the Israel-Iran war started a week ago for what Starmer called "contingency support".
Iran has threatened to attack US, French and British bases in the region if those countries help Israel fend off Iranian strikes.
The defence ministry and police are investigating.
with Reuters
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