© The Author 2015. Published by Oxford University Press. All rights reserved. The proclamation of a marine protected area by David Miliband in the Chagos Archipelago in 2010 triggered a complaint of infringement of sovereignty by Mauritius and a human rights claim by dispossessed Chagossians. It also faced criticism by academia and the UK media. In March 2015, a Tribunal of the Permanent Court of Arbitration investigated the Mauritian claim. In a majority decision, the Tribunal found that Mauritius was legally disabled from pursuing its sovereignty claim but through estoppel the UK Government was required to fulfil its obligations contained in an undertaking given before independence. This included requirements for the return of the Archipelago once it is no longer needed for defence, mineral rights and historic fishing rights. It called for the proclamation to be revoked. The majority of the Tribunal found no link to the exclusion of the Chagossians. It provides useful insight on the development of large marine parks.