Pro-Palestinian activists have broken into RAF Brize Norton and sprayed two military planes with red paint in a major security breach.
Prime Minister Sir Keir Starmer has condemned the action as “disgraceful”, saying that it was an “act of vandalism”.
Footage posted online by Palestine Action on Friday showed two people inside the Oxfordshire airbase in darkness, with one riding on a scooter up to an Airbus Voyager and spraying paint into its jet engine.
The Ministry of Defence, which has also condemned the move, is now expected to conduct a review of security at UK military bases. It is working with Thames Valley Police, which is leading the investigation.
Palestine Action said the activists evaded security and claimed they had put the air-to-air refuelling tankers “out of service”.
However, RAF engineers are assessing the damage and a defence source told the BBC they did not expect the incident to affect operations.
In a statement, a Palestine Action spokesperson said: “Despite publicly condemning the Israeli government, Britain continues to send military cargo, fly spy planes over Gaza and refuel US and Israeli fighter jets.”
RAF Brize Norton serves as the hub for UK strategic air transport and refuelling, including flights to RAF Akrotiri in Cyprus. The air force has conducted reconnaissance flights over Gaza out of the Cyprus base.
The base is encircled by a large perimeter fence, with security camera and sensors in the area in addition to manned security checkpoints. Patrols around the base are also carried out from time to time.
But a defence source said these measures would not have been able to provide complete cover around the large airbase.
Palestine Action has engaged in similar activity since the start of the current war in Gaza, predominantly targeting arms companies. In May, it claimed responsibility for the daubing of a US military plane in Ireland.
The group said the activists who entered RAF Brize Norton used repurposed fire extinguishers to spray red paint into the planes’ engines.
It also said they caused “further damage” using crowbars – though this is not visible in the bodycam footage it provided.
Video shows the activists then roaming around the airbase.
The protesters did not spray paint on the Vespina aircraft – used by the prime minister for international travel – which was also on the base.
The MoD told the BBC that RAF Voyager aircraft had not been involved in refuelling or supporting Israeli Air Force jets.
A spokesman said Voyagers have been used in the Middle East to refuel RAF Typhoon jets involved in the ongoing international efforts to tackle the so-called Islamic State in eastern Iraq and Syria.
They have also been used in operations in the Red Sea in the past in operations against Yemen’s Houthi rebels.
Thames Valley Police confirmed it had received a report about people gaining access to the base and causing criminal damage.
“Inquiries are ongoing to locate and arrest those responsible,” the force said.
Lord West, Labour minister for UK security and former head of the Royal Navy, said earlier that while he was not aware of the full details, the break-in was “extremely worrying”.
“We can’t allow thing like this to happen at all,” he told BBC Radio 4’s Today programme, adding that breaches like it were “really a problem” for national security.
Conservative leader Kemi Badenoch said the security breach was “deeply concerning”.
“This is not lawful protest, it is politically motivated criminality,” she said in a statement.
“We must stop tolerating terrorist or extremist groups that seek to undermine our society.”
Shadow armed forces minister Mark Francois told the BBC any attempt to interfere with the engines of large aircraft was “totally reprehensible”.
He added there were “serious questions for the MoD to answer” about how protesters were able to “gain access to what is supposed to be a secure RAF airbase”.
The local Liberal Democrat MP Charlie Maynard described the activists’ actions as “stupid and dangerous”.
He said the investigations should establish “how this happened and what can be done in future to make sure no further breaches occur”.
