The letter of 11 September 2026 is a three-page cross-party letter on House of Commons letterhead, addressed to Prime Minister Andy Burnham at 10 Downing Street and signed by 71 members of both Houses. It was organised in collaboration with ControlAI and hosted on the organisation's campaign page. Its two asks are that the Prime Minister "evaluate and adopt the legislative framework of the Artificial Superintelligence Security Bill" — the Private Member's Bill Alex Sobel MP introduced three days earlier — and that the Government "commit to working with international partners towards an international agreement prohibiting superintelligent AI."
The letter is an advocacy document written by the bill's supporters. Its characterisations of recent events are the signatories' own and are attributed as such below.
The argument
The letter opens with its conclusion: "The UK should lead an international agreement prohibiting the development of superintelligent AI, while preserving strategic AI ambitions." It then distinguishes AI in general from the capability it seeks to prohibit. AI is described as "the crucial technology of the 21st century, vital to military and scientific applications." Superintelligent AI is treated as a separate category: systems "so autonomous and capable that they would replace and outcompete humans across domains," which "would be threat actors in and of themselves, able to overpower and outmanoeuvre our national security apparatus."
That distinction — a prohibition narrow enough to leave a national AI programme intact — is the letter's organising move and matches the structure of the bill it endorses, which prohibits a defined capability rather than regulating AI development generally (Artificial Superintelligence Security Bill (UK) — bill text as introduced).
The letter's stated occasion is recent events: "a string of alarming AI incidents, including rogue AI systems taking unsanctioned action on the internet and hacking organisations." That characterisation is offered without citation in the letter itself; the campaign page links the 2026 OpenAI agent cyberattacks as its referent. It is the signatories' framing of those incidents, not an independent account of them.
The letter adds testimony from inside the industry, quoting "an AI researcher who resigned over concerns that leading AI companies are 'racing straight to self-improving superintelligence'" and that those building it believe "it could kill us all by the end of the decade." The letter does not name the researcher, and neither quotation is attributable to a named person on the document's authority.
The asks
Two are made, in sequence.
Domestic. The Prime Minister is urged to "evaluate and adopt the legislative framework" of the bill. The letter describes it as "the first legislation prohibiting superintelligence introduced in a legislature anywhere in the world" — ControlAI's framing rather than the narrower G7 claim Sobel made on introduction — and states that it "addresses the security risk while ensuring the UK can pursue its AI ambitions for science, defence, and economic competitiveness."
International. A domestic ban is described as insufficient on its own: "A domestic ban protects Britain from home-grown threats. But to deal with the development of superintelligence abroad, there is no solution but to work with a coalition of partners to prevent the development of superintelligence anywhere in the world." The vehicle the letter identifies is the UK's chairing of the G20 — "Our upcoming presidency of the G20 offers an unmissable window to lead a coalition of the willing" — placed in a lineage with the 2023 AI Safety Summit: "Britain has already shown leadership by hosting the first global AI Safety Summit at Bletchley Park" (Bletchley Declaration (AI Safety Summit, 2023)). The letter states no year for the presidency; ControlAI's campaign page identifies it as 2027.
The closing offer is procedural: "We are available to work with you to make this happen across party lines."
Signatories
The block runs to 71 names, printed in order and by title only, with no party affiliations given and no count stated. Sobel signs first. Roughly half the signatures are from members of the House of Commons and half from peers, the latter including a serving bishop, the Lord Bishop of Hereford. Among the MPs are John McDonnell, Dawn Butler, Richard Burgon, Bell Ribeiro-Addy, Afzal Khan, Yasmin Qureshi, Wera Hobhouse, Richard Foord, Vikki Slade, Pete Wishart, Brendan O'Hara, Chris Law, Graham Leadbitter, Carla Denyer, Ben Lake and Sir Desmond Swayne — the last one of the twenty members drawn in the 2026 Private Members' Bill ballot that ControlAI's contact tool had targeted, and an existing supporter of the campaign. Among the peers are Lord Clement-Jones, Baroness Ludford, Lord McNally, Baroness Bonham-Carter of Yarnbury, Baroness Benjamin, Lord Alton of Liverpool, Lord Rees of Ludlow, Baroness D'Souza, Lord Bird, Baroness Evans of Bowes Park, Baroness Verma, Baroness Browning, Lord De Mauley, Lord Evans of Rainow, Lord Hunt of Kings Heath, Lord Knight of Weymouth, Baroness Ritchie of Downpatrick, Lord Foulkes of Cumnock, Lord Green of Deddington, Lord Mackenzie of Framwellgate, Baroness Uddin, Baroness Gill, Baroness Bloomfield of Hinton Waldrist, Baroness Miller of Chilthorne Domer, Baroness Doocey, Lord Oates and Baroness Berger of Barn Hill.
Lord Clement-Jones, signatory 48, is separately named by ControlAI as the peer who put forward the organisation's drafted amendment to the Cyber Security and Resilience Bill on 1 September 2026 (Source: blog.controlai.org).
Press accounts identified fifteen former government ministers among the signatories; the letter itself carries no such count and signs by title only. Three individuals coverage singled out appear on the block under their titles: Robin Butler, formerly Cabinet Secretary and head of the Home Civil Service, as Lord Butler of Brockwell; Zac Goldsmith, formerly a Conservative environment minister, as Lord Goldsmith of Richmond Park; and Arlene Foster, formerly First Minister of Northern Ireland, as Baroness Foster of Aghadrumsee (Source: theguardian.com).
Two counts in the document are distinct and are frequently merged in coverage. Seventy-one parliamentarians signed this letter. Separately, the letter asserts that over the past two years "a cross-party coalition has grown to 130+ UK parliamentarians and 30+ Canadian lawmakers" recognising the risk — a claim about the size of ControlAI's standing campaign, made by the signatories, not a count of this document's signatures.
A third distinction the letter draws is between signing and endorsing. Stuart Russell, Daniel Kokotajlo, Nobel Peace Prize laureate Beatrice Fihn and Sir Stephen Fry are described as having backed the bill; none is a signatory to the letter.
Reception
The Government responded the day the letter was published. A spokesperson said that while it does not consider the bill's measures to be the right approach, it is exploring whether additional targeted interventions may be needed to address the most significant AI-related national security risks (Source: theguardian.com). Sobel sits with the governing Labour Party; the Government had not supported the policy before the letter (Source: time.com).
ControlAI published the letter and an accompanying account on 12 September 2026 under the heading "70+ UK Lawmakers Urge a Ban on Superintelligence" (Source: blog.controlai.org).
Provenance
Captured 13 September 2026 from the PDF at images.controlai.com, linked from the campaign page at controlai.org, whose own inline viewer does not render extractable text. All three pages and the full signature block were transcribed as printed. The letterhead, date, addressee and named bill-endorser list match the Guardian and ControlAI accounts of the same document. Nine divergences between the primary text and the secondary coverage are recorded in the raw file's ## Source-fidelity notes.
Relationships
- supports: UK Artificial Superintelligence Bill (ControlAI draft, May 28, 2026; introduced September 8, 2026) — the letter's first ask is that the Government adopt the bill's legislative framework
- depends-on: Artificial Superintelligence Security Bill (UK) — bill text as introduced — the instrument whose framework the letter endorses
- related: ControlAI — organised the letter and hosts it
- depends-on: Superintelligence — the letter's category distinction between AI generally and superintelligent AI
- related: Ban Artificial Superintelligence Act (announced 2026) — the parallel US bill; the letter's "130+ UK parliamentarians and 30+ Canadian lawmakers" describes the same standing campaign
- related: Bletchley Declaration (AI Safety Summit, 2023), AI Existential Risk, Frontier AI Governance, Stuart Russell, Daniel Kokotajlo, Sir Stephen Fry
- related: Alex Sobel — first signatory; Human Rights and the Regulation of AI (Joint Committee on Human Rights, HC 160, September 2026) — the Joint Committee on Human Rights report published three days later, whose Recommendation 45 would prohibit the development and provision of very powerful systems such as AGI and ASI; five of the committee's twelve members (Sobel, Afzal Khan, Euan Stainbank, Sir Desmond Swayne and Lord Alton of Liverpool) are signatories of this letter
Sources
- Letter text (Source: images.controlai.com), campaign page (Source: controlai.org)
- The Guardian — "UK lawmakers urge Burnham to back ban on superintelligent AI after chilling warnings", 2026-09-11 (Source: theguardian.com)
- ControlAI — "70+ UK Lawmakers Urge a Ban on Superintelligence", 2026-09-12 (Source: blog.controlai.org)