In late October 1983, a nervous President Ronald Reagan made a phone call from the White House to British Prime Minister Margaret Thatcher. That morning, the USA had, without proper warning to or consultation with, the UK, invaded the Caribbean island state of Grenada. Grenada was member of the Commonwealth, and its Head of State was the HM The Queen. Although the two leaders enjoyed the closest of political relationships, this was not going to be an easy conversation, and the President knew it.
Why? Because Margaret Thatcher believed profoundly in an international order underpinned by the rule of law. The purpose of the US invasion was the removal of a left-wing government that the United States regarded as hostile to their interests and growing increasingly close to Cuba. The Thatcher recognised that international law functions as a bulwark for sovereign independence. If powerful allies reserve the right to intervene whenever expedient, the rules protecting smaller and medium powers inevitably weaken. Law, in this sense, does not constrain sovereignty; it enables it.
Fast forward to 2026, The international legal order is entering a period of profound strain. The escalating conflict involving Iran has not merely reignited regional instability; it has exposed a deeper uncertainty about the continued authority of international law itself. The question is not whether international law still matters, but how we can preserve and modernise it in circumstances where even close allies appear increasingly willing to act beyond its traditional constraints.
Britain has long understood that international law is not an abstract moral project. It is an instrument of statecraft. It protects sovereignty precisely because it restrains power. That insight formed a central pillar of post-war British foreign policy and remains highly relevant today. The postwar political generation rightly decided that the era of strong men seeking to divide the world into spheres of influence was inimical to peace and economic prosperity, and instead shaped new institutions underpinning an international, rules-based system that until recently, enjoyed support.
The present confrontation with Iran is proving to be a revealing window on a troubling new world order. Increasingly, international law is seen by major countries such as the US as an obstacle to decisive action, rather than a means of facilitating it. When major powers normalise military action without broad international consensus, the legal threshold governing force gradually erodes. The force of law does not collapse overnight, but it is weakened through repeated exceptions.
For middle powers such as the United Kingdom, this erosion carries strategic consequences. Britain depends upon predictable legal norms far more than it depends upon unilateral military dominance. A world governed primarily by power politics diminishes British influence.
Competing claims of anticipatory self-defence, deterrence and regional security have been advanced to justify military action against Iran. Yet the legal basis for such operations remains contested. Proper leadership in the international law sphere, however, is not merely meek acceptance of the status quo. Sometimes, the margins have to be pushed. The 1945 UN Charter framework, built upon the prohibition of the use of force except in cases of self-defence or Security Council authorisation, struggles to accommodate modern security threats involving proxy actors, cyber operations and long-range strike capabilities. The law of imminent threat is still more or less what it was in the late 1830’s, when the leading legal authority on it was decided.
Complicating matters further is growing domestic scepticism toward international institutions, including the United Nations system and the European Convention on Human Rights. Critics argue that international law has expanded beyond state consent, sometimes appearing detached from democratic accountability.
These concerns cannot simply be dismissed. International law loses authority when it appears to override legitimate national decision-making without clear justification.
Yet withdrawal from international frameworks would represent strategic self-harm. Britain benefits disproportionately from systems grounded in treaty obligation, judicial process and predictable dispute resolution.
It is sometimes assumed that strong national sovereignty sits uneasily alongside international legal obligation. British history suggests the opposite. Despite her close personal and political relationship with Reagan, Thatcher expressed serious reservations about the legality of the intervention and declined British participation. Her objection was based on belief in the rule of law. This remains a lesson worth relearning. Loyalty within alliances must never mean abandonment of legal principle.
Britain should adopt what might be termed principled legal leadership; maintaining our alliances whilst being clear about the need for lawful justification and institutional legitimacy. This approach has historical precedent. British diplomacy has often exercised influence precisely by shaping legal frameworks rather than dominating military outcomes. Taking the longer view, the Congress of Vienna in the aftermath of the Napoleonic War is a great example of this, and it was repeated regularly at key moments throughout the 19th century.
Coming back to the present, the task must be reform rather than immediate retreat. International law should be anchored in three principles:
- State consent as the foundation of legitimacy.
- Judicial restraint to preserve public confidence.
- Adaptability to address new forms of conflict, particularly cyber warfare and hybrid threats.
As cyber operations, proxy warfare and remote strikes challenge traditional definitions of armed attack and self-defence, Britain should lead efforts to clarify these doctrines internationally. This should include:
- Developing clearer legal standards governing cyber operations equivalent to armed attacks.
- Establishing multilateral understandings on pre-emptive self-defence against emerging technological threats and properly updating the concept of imminent threat.
- Strengthening mechanisms for independent fact-finding following contested military actions.
Principled independence enhances British strategic weight. Other countries listen to a country perceived as one guided by law rather than convenience. Our legal tradition, diplomatic network and reputation for constitutional seriousness continue to command respect, but if Britain applies legal standards selectively, by invoking international law against adversaries while overlooking breaches by allies, then our authority will rapidly erode.
A renewed British approach to international law should therefore rest upon four commitments:
- Defend the prohibition on aggressive war, even when politically inconvenient.
- Promote institutional reform, ensuring international courts operate within clear mandates.
- Modernise legal doctrine to address cyber and hybrid conflict.
- Exercise candid alliance diplomacy, offering legal counsel rather than automatic approval.
The Iran conflict has revealed a world edging toward legal uncertainty. Yet history shows that international law has survived previous crises precisely because states recognised its importance.
Britain’s national interest lies neither in nostalgic and unthinking attachment to outdated institutions by unimaginative and managerial politicians of the left nor in unthinking Faragiste cheerleading for a purely power-based order. Our task is more demanding: to act as a steward of lawful international conduct while adapting the system to contemporary realities.
Margaret Thatcher grasped that sovereignty is strongest when exercised within a framework of rules that bind all states, powerful and weak alike. That insight remains as relevant today as it was forty years ago. In an age of geopolitical turbulence, Britain should once again lead not by abandoning international law, but by renewing it with confidence, pragmatism and in defence of sovereign independence itself. It is the centre-right of British politics that is best-placed to deliver this approach.
This article was written by Rt Hon Sir Robert Buckland KBE KC, who has supported Prosper UK since its launch and previously served as Secretary of State for Justice. The views expressed are his own and do not necessarily reflect those of Prosper UK.