Two sentences, delivered a day apart, define Britain's entire legal position in the war against Iran. On 28 February, as American and Israeli aircraft opened their campaign, the prime minister told the country the United Kingdom was not involved in the strikes on Iran. On 1 March he told it that the United States had requested permission to use British bases for a specific and limited defensive purpose, and that we have taken the decision to accept this request. Both sentences were deliberate. The distance between them is the position.
Unlike almost any other British military commitment of the past two decades, this one came with its reasoning attached. Downing Street published a summary of the government's legal position on the day the permission was granted, an unusual step taken in explicit recognition, the prime minister said, of the country's memory of Iraq. What follows is that position as London has actually stated it, the international law it stands on, and the places where outside lawyers say it blurs.
What London has said on the record
The 1 March statement, delivered by Sir Keir Starmer, fixed the purpose before the permission. Iran, the prime minister said, was launching sustained attacks across the region at countries who did not attack them, hitting airports and hotels where British citizens were staying, with at least 200,000 British citizens in the region and a military base in Bahrain narrowly missing British personnel the day before. British jets were already in the air intercepting Iranian strikes. The only way to stop the threat, the statement continued, is to destroy the missiles at source, in their storage depots or the launchers which used to fire the missiles. That was the purpose for which the American request was accepted, and the statement named its legal basis: the collective self-defence of longstanding friends and allies, and protecting British lives, in accordance with international law.
The published legal position carried the same architecture in the government's own legal vocabulary. The UK is acting in the collective self-defence of regional allies who have requested support, and the UK and its allies are permitted under international law to use or support force where acting in self-defence is the only feasible means to deal with an ongoing armed attack and where the force used is necessary and proportionate. The American request would facilitate specific and limited defensive action against missile facilities in Iran which were involved in launching strikes at regional allies. The statement closed the door it did not want opened: nothing in the position signals wider involvement in the broader conflict between the United States, Israel and Iran, and the government will notify the Security Council of relevant actions under Article 51 of the Charter.
Under Prime Minister Andy Burnham the policy was not altered. The Guardian reported in July that the extension of the agreement had been notified to the new prime minister, which makes the permission, as of the seventh month of the war, a decision of two successive governments.
What the permission is, in law
The legal relationship underneath the politics is old and well understood. American forces do not operate from British bases at their own discretion; under the arrangements governing visiting forces, the United States must seek permission before using British military installations for its operations, and Britain can refuse. That veto is the fact from which everything in the position derives, including its dangers.
The government's initial answer to the American request shows what the veto was being used for. Reporting gathered by Aurel Sari, the legal scholar whose analysis for Just Security remains the fullest public account, records that the United States had previously been refused, on the Attorney General's advice, for two reasons: that supporting an unlawful use of force could make the UK complicit in an internationally wrongful act under the law of state responsibility, and that allowing British territory to be used for an act of aggression against Iran would itself amount to aggression by the United Kingdom under the General Assembly's Definition of Aggression, whose article 3(e) treats permitting a state whose territory it is to be used by another state for perpetrating an act of aggression against a third state as an act of aggression by the host. Those are not archaic concerns. They are the reasons the government's lawyers drew a line in February, and the permission of 1 March is best understood as a mapping of exactly where that line now runs.
The line is a purpose test. If the use of British territory serves the collective self-defence of states that have been unlawfully attacked and have requested help, the consent is effective, the assistance is lawful, and the hosting is not aggression. If the same territory serves an offensive campaign against Iran, the February objections reassert themselves in full. The whole position, published and unpublished, lives inside that distinction.
Where outside lawyers say the line blurs
The critique has been consistent since March, and it is not political. Chatham House's analysis, published the week after the permission, is titled on its own terms as an argument that the UK's arguments blur the line between lawful self-defence and unlawful war. The legal journalist Joshua Rozenberg, one of the few commentators who read the legal position closely when it appeared, framed his critique around its central qualification: Britain will defend its allies, but only if they were not previously involved in the conflict. The human rights organisation Human Rights Watch wrote to the Attorney General on 23 March seeking clarification of the safeguards ensuring respect for international law in the American operations launched from British bases, and in the Commons debate on the Middle East the same week, the government's own formulation, that a legal basis is the third principle of its decisions, sat in a debate dominated by the question of what that basis covers.
Sari's analysis, which marshals the position's problems most completely, makes three points worth stating precisely. The first concerns the nature of the supporting role. Defensive intercepts over the Gulf are one thing, and British aircraft have flown them. Strikes by heavy bombers on missile storage depots and launchers inside Iran are another: the targets are dual use, the defensive purpose is asserted rather than policed, and the further the operations extend, the harder it becomes to distinguish supporting defence from participating in a campaign whose stated objectives, in the American account, include destroying Iran's missile industry and more. The second concerns complicity. If the underlying American and Israeli use of force exceeds lawful self-defence, assistance to it engages the responsibility of the assisting state, which is precisely the concern the February refusal had acted on. The third is the quiet implication of the government's own framing: by describing Iran's attacks on the Gulf states as unlawful while declining to call the campaign against Iran lawful, the position implies that Iran retained a right of self-defence that its conduct has since exceeded. That is a defensible reading, and it is also the reading Iran's own pronouncements reject, since Iran has formally invoked self-defence and declared all bases, facilities and assets of hostile forces in the region to be legitimate military targets.
What no critic disputes is the government's honesty about its own structure. The permission, the published summary and the prime minister's statement all draw the same line and all claim to hold it. The dispute is about whether that line, in Sari's phrase, can actually be walked.
The Attorney General at the centre of it
No account of the position can omit the man whose advice produced its shape. Lord Hermer, the Attorney General and Lord Chancellor, entered office as the most publicly identified exponent of international law in any recent British government, his formulation that international law is the rule of law writ large having drawn criticism from figures close to the American administration before the war began. In January, the Guardian reported his view that the UK is entitled to weigh diplomacy before calling out allies on international law breaches, the defender's version of a consistent doctrine. The February refusal of the American request was, on the reporting, taken on his advice, and the March permission carries the grammar of a lawyer marking out a defensible boundary: specific, limited, defensive, notified.
The critique of him has followed the same arc. Rozenberg's piece, published the day after the permission, addresses the position's weakness directly, and the broader commentary, in Britain and among European lawyers watching the first war of the second Trump administration, has treated the British position as the test case for whether the law of the Charter survives its friends. What neither side disputes is that the advice mattered: the veto was used, then used differently, and the difference is a legal decision, not a military one.
What the Fairford arrests did to the position
The position's premises were built for the Gulf, and the war has been relocating them. Iran's Revolutionary Guard declared on 23 July that any base used for aggression against Iranian territory constitutes a legitimate target, naming Fairford, from which American bombers had launched missions two days earlier, and the government's reply insisted the armed forces act in accordance with international law and are not getting drawn into the wider conflict. Sixty six days later, five men were arrested on suspicion of preparing a terrorist act in the village beside that base, bomb robots examined three vans, and counter terrorism police began investigating whether Iran was behind it. Nothing has been established about origin, and the government has urged against speculation.
What the episode changes is the position's operating environment. The legal line between defensive and offensive was always drawn in London; the IRGC's warning and the arrests demonstrate that the risk attached to the hosting is now drawn in Gloucestershire, where the base's neighbours have reported the bombers shaking their houses since March. The position's own terms, collective self-defence of allies, protection of British lives, necessity, proportionality, were drafted to justify destroying missiles aimed at the Gulf. The same documents now justify a forward bomber base that Iran has named, and the next article of the position, unwritten, is what the government's obligations to the base's own village would be if the investigation ever ended in charges.
The threads the position leaves hanging are the same ones its own publication flagged. The Security Council notification promised under Article 51 is a commitment whose exercise the public record does not document. The distinction between defensive and offensive operations has been tested by seven months of extensions and widening target sets without any public account of where it now runs. And the question the February refusal raised, whether Britain would ever call the campaign it assists unlawful, has been answered only by silence. A position that exists in published words has, so far, held the war off its own text. That is more than most wartime positions manage, and less than its critics require.