In the early hours of Friday, activists from the protest group Palestine Action infiltrated RAF Brize Norton in Oxfordshire. Using electric scooters, they navigated the vast airbase under the noses of unsuspecting security personnel. Brize Norton is a critical part of Britain’s defence infrastructure: a military Heathrow, used for trooping flights, freight and refuelling. The activists, who uploaded video footage of their raid to social media, subsequently vandalised two Voyager air-to-air refuelling tankers, damaging them with crowbars and spraying paint into the engine’s turbofans using adapted fire extinguishers. They claimed, nebulously, that their intention was to disrupt British military support for Israel.

Then, something possibly more remarkable happened. By Friday evening, sources within the usually glacial Home Office indicated that Home Secretary Yvette Cooper would ask Parliament to make Palestine Action a proscribed organisation under the Terrorism Act. This is no small step, especially within just 24 hours of what activists describe as “non-violent direct action”. Membership or support for a proscribed organisation carries a maximum sentence of 14 years.

Furthermore, Palestine Action is the first Left-wing domestic “extremist” group to be so proscribed. What, then, is the significance of the Home Secretary’s decision? Critics, of whom there will be many, will argue proscription is heavy-handed and disproportionate. They will say it provides evidence of a government seeking to criminalise protest. This interpretation seems strange, given the Met’s tolerance of controversial pro-Gaza rallies and skateboarding escapades with Extinction Rebellion.

British courts must bear responsibility for creating a permissive environment for such activism. In 1996, Campaign Against the Arms Trade (CAAT) activists vandalised a BAE Hawk aircraft. The group used a defence of reasonableness, arguing that the aircraft would be used by the Suharto regime in Indonesia to bomb civilians in East Timor. Therefore, “criminally” damaging them was lawful. They were acquitted of all charges.

The “Fairford Five”, who vandalised US Air Force property in 2003, used an identical defence (while one member was represented by a human rights barrister called Keir Starmer). They walked free, the jury failing to reach a verdict. Other judicial decisions — for example the Zeigler ruling on the lawfulness of highway obstruction, have emboldened activist groups.

This novel interpretation of law feeds into the wider charge of “two-tier” policing, one to which the Government seems increasingly sensitive. This most likely informs the Home Office decision, as many Britons believe that demonstrators have been routinely indulged while blocking motorways and busy city streets. This isn’t to say that Palestine Action shouldn’t necessarily be proscribed for inciting “extreme actions”. Richard Barnard, a founding member, is currently facing trial for supporting Hamas at protests.

Friday’s action — breaking into an RAF base, at a time of raised international tension, and disabling military aircraft — was an escalation. Activism or sabotage? Terrorism and counter-extremism analysts will draw comparisons between today and the Seventies: a young, university-educated generation, radicalised by war (Vietnam then, Gaza now) and inculcated to loathe Western capitalism (Trotskyist Marxism then, postmodern Marxism now), begin the slide from political action to political violence.

The Home Office counter-terrorism secretariat will no doubt have put in the hours this weekend. Yet a sublime instance of cosmic irony means the radical’s lawyer of choice, Attorney General Richard Hermer, will cast his eye over the proscription. Will he feel his usual urge to meddle? And how will the Labour Left react when Cooper puts her case to Parliament? Either way, a line in the sand is being drawn. The politics go beyond Palestine Action, which will now discover the meaning of the acronym FAFO. There will be more protests and activism which test the strength of this new Home Office stance. The question is: do they draw back or double down?