Britain claims sovereignty over the Chagos Islands, but three powerful UN bodies have ruled that the archipelago is part of Britain’s old colonial empire and should be handed to Mauritius immediately.

The boat – due to conduct scientific research – is also carrying a group of elderly Chagossians who were forced by Britain to leave their homes on Chagos half a century ago.

The pretext for this boat trip is science. And the Mauritian government is planning to map reefs in the waters around the remote Chagos Islands.

But this is a highly political – some would say – provocative move by Mauritius, which is, increasingly, seeking to assert what it maintains is its rightful claim to the archipelago.

Britain says Mauritius can have Chagos back when it is no longer needed for security purposes.

One of the islands, Diego Garcia, is home to an important American military base.

But, with world opinion – at the UN and elsewhere - now shifting firmly behind Mauritius, Britain is under growing pressure to hand the Chagos Islands over now.

The UK's foreign office has been informed about the boat trip.