The National Security Bill 2026 creates three new criminal offences: mass-casualty attack planning without ideological motive, extreme violent material offences, and measures targeting hostile state-backed organisations. This guide explains each offence, relevant legal frameworks, human rights implications, and tracking points as the bill progresses through Parliament.
Criminal practitioners, public-law specialists, online safety lawyers, in-house counsel at platforms, sanctions and national security advisers, human rights specialists and law students preparing commercial-awareness or public-law content. Updated as the bill develops.
Background: the Southport attack and the Hall review
The proposals respond to recommendations made by Jonathan Hall KC, the Independent Reviewer of Terrorism Legislation, in his March 2025 review on classification of extreme violence used in the Southport attack on 29 July 2024.
The Southport attacker, Axel Rudakubana, killed three young girls and injured eight more at a Taylor Swift-themed dance class. The case raised a difficult question about how the criminal law should categorise extreme violence carried out by lone individuals without an ideological motive.
Hall’s review concluded that the existing terrorism definition under section 1 of the Terrorism Act 2000 should not be changed. He found the definition was already wide and expanding it could lead to inaccurate use and unacceptable restrictions on freedom of expression. Instead, he recommended a new bespoke offence to fill the gap.
What is being proposed?
Mass-casualty attack planning
The bill is expected to criminalise preparation by an individual to carry out a mass-casualty attack where the intention is to kill two or more people. The offence would not require an ideological motive. Hall recommended a maximum sentence of life imprisonment, adapted from terrorism legislation but designed to operate outside it.
The offence is intended to close what Hall described as a real gap for lone individuals who plan mass killings outside the terrorism framework. He gave examples of around ten lone-actor cases involving extreme violence that were not prosecuted as terrorism.
Extreme violent material
The bill is reported to create new offences relating to extreme violent material. This may cover creating, sharing or possessing content that glorifies serious violence. The detail of any thresholds, exceptions and mental elements will not be known until the bill text is published.
Hostile state-backed groups
The bill includes measures targeting organisations linked to espionage, sabotage or interference by hostile states. This builds on the existing framework under the National Security Act 2023, which already created offences for foreign interference and established the Foreign Influence Registration Scheme.
How does this fit with existing law?
Terrorism Act 2000
Section 1 of the Terrorism Act 2000 defines terrorism as the use or threat of action where the action is designed to influence the government or intimidate the public, and is made for the purpose of advancing a political, religious, racial or ideological cause.
The ideological motive requirement is central. Hall confirmed in his review that this requirement could not be applied to the Southport attacker because there was no evidence the attacker’s purpose was to advance a political, religious, racial or ideological cause. The Crown Prosecution Service reached the same conclusion.
National Security Act 2023
The National Security Act 2023 created new offences for espionage, sabotage and foreign interference. It established the Foreign Influence Registration Scheme requiring registration of political influence activities and additional registration for activities directed by specified foreign powers.
The new bill is expected to expand the toolkit by adding proscription or disruption powers targeting state-backed organisations operating in the UK.
Online Safety Act 2023
The Online Safety Act 2023 imposes duties on online platforms in respect of illegal content. The interaction between the new offences and platform takedown duties under the Online Safety Act will need to be worked out as the bill progresses. Ofcom’s role as the online safety regulator is relevant here.
What human rights issues arise?
Article 10: freedom of expression
Article 10 of the European Convention on Human Rights protects expression, including expression that offends, shocks or disturbs. Restrictions must be prescribed by law, pursue a legitimate aim and be necessary in a democratic society.
Hall’s review itself raised concerns about Article 10. He warned that broadening the criminal law could create unacceptable restrictions on freedom of expression. The new offences relating to extreme violent material in particular will be examined for their Article 10 compatibility.
Article 8: private life
Article 8 protects private and family life. Restrictions on accessing material online, on retention of material or on associations with particular groups can engage Article 8. Any new offence relating to possession of extreme violent material would need to address Article 8 questions.
Mental element and preparatory acts
For the mass-casualty offence, the dividing line between protected thought, planning and criminal preparation will be central. The mental element required, the nature of preparatory acts caught and the safeguards in place will be subject to intense scrutiny.
How will the offences be defined?
The detail of the offences is not yet known. Practitioners should watch for the following when the bill is published:
- The threshold for “preparatory steps” in the mass-casualty offence.
- The mental element required, including any specific intent to kill two or more people.
- The definition of extreme violent material and any thresholds for criminal liability.
- Defences and exceptions, particularly for journalistic, academic or research purposes.
- The interaction with existing terrorism offences and how prosecutors will choose between regimes.
- Police powers of arrest, search and seizure under the new framework.
- The proscription mechanism for state-backed organisations, including the standard of proof and judicial oversight.
What should practitioners do now?
Criminal defence solicitors
Familiarise yourself with the existing Terrorism Act 2000 framework and the case law on preparation offences under section 5. Watch for the bill text and any sentencing guidelines. Consider how the new offence will affect plea advice, mode of trial and disclosure.
Online safety and platform lawyers
Review existing client compliance arrangements against the likely shape of the new offences. Consider how takedown duties under the Online Safety Act may interact with new criminal offences. Brief clients on the policy direction and prepare for revised content moderation protocols.
Public law and human rights practitioners
Engage with select committee inquiries and the Joint Committee on Human Rights. Track the Article 10 and Article 8 dimensions of the bill. Consider judicial review implications if the proscription mechanism for state-backed organisations is challenged.
In-house counsel
Brief boards on the policy direction. Identify exposure points: content hosted on platforms, international supplier relationships that may engage hostile-state provisions, employee training on extreme violent material policies.
Common mistakes to avoid
- Treating the King’s Speech announcement as enacted law. The bill text and Royal Assent are still ahead.
- Conflating the new mass-casualty offence with terrorism. Hall specifically recommended a separate framework precisely to keep them distinct.
- Underestimating the human rights challenges. Article 10 in particular will shape parliamentary scrutiny.
- Assuming the offences will apply only to clear-cut cases. The definitions and thresholds will determine reach.
- Ignoring the online safety dimension. Platform compliance will be central to enforcement.
What to watch for next
The bill text and explanatory notes when published by the Home Office. The section 19 statement of compatibility under the Human Rights Act. Pre-legislative scrutiny by relevant select committees. The Joint Committee on Human Rights legislative scrutiny report. Law Society, Bar Council and Criminal Bar Association briefings as they emerge.
The Online Safety Network and digital rights organisations will also be active on the Article 10 dimensions. Engaging with consultation processes when they open will be important for firms with relevant practice areas.
Useful sources
- Jonathan Hall KC’s Independent Review on Classification of Extreme Violence (March 2025).
- The National Security Act 2023.
- The Terrorism Act 2000.
- The Online Safety Act 2023.
Last updated: 15 May 2026.