At the heart of the Britain-US dispute over Iran lies a profound question about sovereignty — specifically, the degree to which a country that is deeply embedded in a military alliance retains genuine freedom of action in decisions about military cooperation. Britain’s experience raised that question in vivid and public terms.

Formal sovereignty is clear: Britain is an independent country, with its own parliament, its own foreign policy, and its own military. No one disputes that it has the legal right to decide whether to grant or withhold permission for foreign forces to use its territory. The initial refusal was an exercise of that legal authority.

But practical sovereignty is more complicated. Countries that rely on alliance membership for their security — and that have built their foreign and defence policies around those alliances — face significant constraints when they seek to exercise their formal autonomy in ways that conflict with alliance expectations. The constraints are not legal but political and diplomatic.

Britain discovered those constraints in the most public possible way. The cost of exercising its formal sovereignty — refusing a request from its closest ally — was a presidential rebuke, a damaged relationship, and a reversal that suggested the original decision had been unsustainable.

The question the episode raised — about the nature of sovereignty in an age of deep alliance entanglement — is one that does not admit of easy answers. But it is one that Britain, like other allied nations, will need to address more explicitly as the pressures and demands of alliance membership continue to evolve.