Greta Thunberg detained under UK Terrorism Act in central London on Dec. 23, 2025, after police said a placard she held could be seen as support for proscribed group Palestine Action; she was later released from custody.
What happened in London
Greta Thunberg, 22, was detained during a pro-Palestinian rally in the City of London’s financial district on Tuesday, Dec. 23, 2025, according to the protest organisers and police statements describing the arrest of a 22-year-old woman.
City of London Police said the arrest was linked to displaying an item in support of a proscribed organisation, referencing Palestine Action, and the alleged offence cited was Section 13 of the Terrorism Act 2000.
Video shared by campaigners showed Thunberg holding a sign reading: I support the Palestine Action prisoners. I oppose genocide.
The protest was tied to support efforts for jailed activists linked to Palestine Action, and it took place outside offices connected by organisers to the insurance of a defence firm.
Police also reported arrests and an investigation connected to alleged criminal damage in the area (including paint-related vandalism) around the same time.
Later on Dec. 23, Thunberg was released from police custody, according to reporting citing the campaign group’s account of events.
Key timeline
| Date (2025) | Development | Why it matters |
| 23 Jun | The Home Secretary confirmed intentions to proscribe Palestine Action in a written ministerial statement (as referenced by UK policing guidance). | Marks the formal start of the proscription pathway that later shaped protest-related arrests. |
| 30 Jun | UK government announcement said three groups were set to be proscribed, including Palestine Action. | Public confirmation that proscription was imminent and would create new criminal offences. |
| 5 Jul | Proscription came into force at 00:01, making membership and some forms of support criminal offences. | Changes the legal risk for signs, slogans, and materials that could be interpreted as support. |
| 23 Dec | Police detained Thunberg under Terrorism Act powers tied to alleged support for a proscribed organisation. | Escalates the debate about protest, speech, and counter-terror law enforcement. |
| 23 Dec | Thunberg was released from custody later the same day. | Suggests the case may continue through review, bail, or charging decisions (depending on evidence). |
Why police used the Terrorism Act
Police pointed to Section 13 of the Terrorism Act 2000, which makes it an offence in a public place to wear, carry or display an article in a way that creates reasonable suspicion a person is a member or supporter of a proscribed organisation.
Section 13 also covers publishing an image of such an article in circumstances that arouse reasonable suspicion of membership or support.
The maximum penalty for a Section 13 offence is up to six months’ imprisonment and/or a fine, under the statute.
The UK government’s public guidance on proscription explains that proscription makes it a criminal offence to display articles in a way that creates reasonable suspicion of membership or support (Section 13), alongside other offences such as membership and inviting support.
That same guidance states Section 13 has a maximum penalty of six months in prison and/or a fine not exceeding £5,000.
In Thunberg’s case, police indicated the placard was the item at issue, and the organisation referenced was Palestine Action, which authorities treated as proscribed.
What proscribed means in practice
The Home Secretary may proscribe an organisation if they believe it is concerned in terrorism and proscription is proportionate, according to UK government guidance on the Terrorism Act 2000 framework.
The same guidance lists proscription offences that can apply, including membership (Section 11), inviting support (Section 12), and displaying articles (Section 13).
A ProtectUK policing guidance note said the Terrorism Act proscription of Palestine Action came into force on July 5, 2025.
Who is Palestine Action—and what changed in 2025
A UK government announcement on June 30, 2025 said Palestine Action would be among three groups set to be proscribed following advice from cross-government experts.
An explanatory memorandum on the proscription order states the order added Palestine Action (alongside two other groups) to the list of proscribed organisations in Schedule 2 to the Terrorism Act 2000.
ProtectUK’s policing guidance described proscription as making it a criminal offence to be a member of the group or to invite or recklessly express support, and it also highlighted that the legislation took effect at 00:01 on July 5, 2025.
In the days leading up to Thunberg’s detention, campaigners said the demonstration aimed to support prisoners linked to Palestine Action and to spotlight companies allegedly connected to defence-sector activity.
Police and campaign groups framed the Dec. 23 London event as part of a broader pattern of protests responding to the proscription decision and related prosecutions.
The result is a new enforcement reality where protest signage can be assessed under counter-terror legislation if it is interpreted as signalling support for a proscribed organisation.
Reactions and legal debate
A UN human rights statement in July warned the Palestine Action proscription raised concerns about counter-terrorism laws being applied to conduct not terrorist in nature, and it cautioned about impacts on fundamental freedoms.
Supporters of the protest described Thunberg’s detention as part of a clampdown on activism linked to Gaza solidarity campaigning and opposition to the proscription.
Police, meanwhile, framed the matter as enforcement of proscription offences tied to the display of items that could reasonably be read as supporting a proscribed group.
Thunberg has previously faced UK protest-related legal action, including an earlier case where a judge found police lacked authority in that specific set of circumstances (separate from the Dec. 2025 incident).
The new element in 2025 is the proscription status and the specific offence basis (Section 13) linked to suspected signalling of support for a proscribed organisation.
This has intensified scrutiny around how reasonable suspicion is assessed when the “article” is a political placard and the setting is a public demonstration.
What police must prove (Section 13)
| Element | What the law focuses on | Why it matters for placards |
| Public place | The offence applies in a public place. | Protests typically occur in public, so this condition is often met. |
| Article displayed | The person wears, carries or displays an article. | A sign/placard can qualify as an article. |
| Reasonable suspicion | Display must arouse reasonable suspicion of membership/support for a proscribed organisation. | The case can hinge on wording, context, and perceived endorsement. |
Final thoughts
Thunberg’s detention—and subsequent release—keeps attention on how UK counter-terror provisions are being used in street-level policing of demonstrations, especially when proscribed organisations are referenced on signs.
Further updates are likely to depend on whether police seek charges, whether prosecutors consider the Section 13 threshold met, and whether courts clarify how reasonable suspicion applies to protest messaging.
Separately, legal and rights-based challenges to the 2025 proscription decision continue to shape the wider context in which these arrests occur.
