The naval base on Diego Garcia in the central Indian Ocean is one of the most strategically important U.S. military installations in the world. But the base’s future might just have been thrown into question by a seemingly unrelated international ruling that the British government, which is sovereign over Diego Garcia, acted illegally by unilaterally announcing the creation of an environmental protection zone in the territory back in 2010.

Diego Garcia is the largest island of the Chagos Archipelago, a British Overseas Territory that also happens to be claimed by neighboring Mauritius. In April 2010, London declared the creation of a “no-take” marine protected area (MPA) in the entire archipelago (except for a three-mile exemption around the base on Diego Garcia) ostensibly in order to better protect the “pristine” coral reefs of the Great Chagos Bank—the largest coral atoll structure in the world. The proposal was supported by high-profile environmentalist groups like Pew Environment and Greenpeace, and had been cleared with top U.S. officials in advance of the announcement.

The problem is that Mauritius never consented to the creation of the MPA. Pointing to the UN Convention on the Law of the Sea, Port Louis insisted that London had a duty to take its legitimate interests in Chagos into consideration before making consequential decisions regarding the territory’s governance—not least of all because London has formally undertaken to cede the islands, including Diego Garcia, to Mauritius once they are no longer needed for military purposes. Britain dismissed Mauritius’s claims and pressed ahead with the MPA.

But in its ruling, the permanent court of arbitration in The Hague has endorsed the Mauritian point of view—that is, it was illegal for Britain to act unilaterally in Chagos by not properly consulting Mauritius. After all, if all parties agree that Mauritius will one day govern the territory, then it stands to reason that Port Louis has a very real interest in what happens in Chagos in the meantime. As such, steps should have been taken to ameliorate Mauritian concerns regarding the MPA. Britain had no right to act unilaterally.

This ruling—which, importantly, is binding on both parties—could have potentially wide-ranging implications for the future of the base on Diego Garcia. For if Britain acted illegally by creating a relatively benign marine protection zone in Chagos, would it not also be illegal to act unilaterally to take much more portentous decisions regarding the future of the U.S. military in the archipelago? Far from being a hypothetical scenario, this question is actually of critical importance, given that the present executive agreement governing U.S. usage of Diego Garcia is up for renewal in 2016 and so will have to be renewed imminently.

As a general rule, London has always governed the Chagos Islands in a way that grants the U.S. military the maximum possible leeway. Legal restrictions on what the United States can and cannot do on Diego Garcia are few and far between. Indeed, the plan to create an MPA in Chagos was sold to U.S. officials partly on the grounds that it would help to buttress this legal and political “black hole.”

Contrary to British officials’ faithful intentions towards their American counterparts, however, it turns out that London might have dropped the ball in quite spectacular fashion. Instead of safeguarding the future of the naval facility on Diego Garcia—an alleged black site, it should not be forgotten—the decision to push through the Chagos MPA against regional opposition appears to have achieved the exact opposite outcome. International and domestic pressure to rethink the political arrangement regarding Diego Garcia is bound to mount now that Britain has been found in breach of international law, especially given renewed interest in allowing the indigenous population of the islands to resettle their homeland after fifty years in exile. In short, the future of Diego Garcia is in greater doubt now than at any other time in its history. And the quandary is entirely of London’s own making.