The UK wants to extend its territorial rights around Ascension Island in the Atlantic.
Countries have ownership of their underwater resources lying within 200 nautical miles from their shorelines.
However, Britain argues that Ascension’s landmass extends much further underwater, resulting in a greater territorial claim.
Ascension Island forms part of the British overseas territory of St Helena.
Britain will present its case to the United Nations Commission for the Limits of the Continental Shelf in New York today.