Exiled Indian Ocean islanders on Tuesday lost a British court challenge launched to prevent Britain from setting up a marine park they suspect is aimed at stopping them from ever returning.

Former residents of the Chagos Islands archipelago in British Indian Ocean Territory say the move to establish a marine protected area (MPA) -- which involves a ban on commercial fishing -- would effectively prevent them from resettling the atolls.

Britain expelled the Chagossians between 1967 and 1973, relocating them to Mauritius and Seychelles, to allow the United States to establish a naval and air base in the Indian Ocean.

The exiled Chagossians have fought a long series of legal battles for the right of return.

The Chagos Refugees Group claimed the proposed marine area -- the world's largest -- was legally flawed.

But at the High Court in London, judges Stephen Richard and John Mitting ruled that the marine park was indeed "compatible with EU law".

The vast reserve was created by the territory's commissioner Colin Roberts on the instructions of the then-foreign secretary David Miliband in April 2010.

Lawyers for the islanders said a classified US government cable leaked by anti-secrecy website WikiLeaks supported their accusations.

They said Roberts was reported telling American diplomats at the US embassy in London in May 2009 that the MPA would keep the Chagossians from resettling the islands and mean "no human footprints" in the territory.

In cross-examination, Roberts denied that the marine park was declared for the "improper purpose" of keeping the Chagossians out, saying it was created for environmental and conservation purposes.

He refused to answer questions about the authenticity and accuracy of the cable.

The judges ruled that British law incorporating the 1961 Vienna Convention on Diplomatic Relations meant the alleged cable was inadmissible in evidence.

Richards said "a truly remarkable set of circumstances" would have to have existed for the case on improper purpose to be right.

"Those circumstances would provide an unconvincing plot for a novel," he ruled.

Sam Brown, from the Clifford Chance law firm representing the Chagossians, said the ruling effectively banned documents aired by WikiLeaks from being used in English courts.

The exiled islanders said in a statement: "This is disappointing to Chagossians, some of whom will no longer be able to sustain themselves by continuing our traditional fishing rights, which is the only link we are allowed with our homeland since the UK unlawfully expelled us from our islands.

"Our return will not endanger the beautiful corals or remaining fish stocks in any way.

"We shall accordingly continue our fight for justice and we are strongly convinced that ultimately victory will be ours."

They said they were considering whether to appeal.

The British Indian Ocean Territory lies some 500 kilometres (300 miles) south of the Maldives.

The main island, Diego Garcia, is now populated by US military personnel, civilian contractors and some British service personnel. They number a few thousand in total.