Almost four decades after Britain evicted 2,000 Indian Ocean islanders to make way for American stealth bombers and B-52s, the dispossessed are appealing to London's High Court to overturn a royal decree that bars them forever from returning to their homes.

They’ve been here before. Just five years ago, their lawyers humiliated the British establishment by winning a case that ruled there was no legal justification for the expulsion of these “Tarzans” and “Men Fridays”, as diplomats dubbed their distant subjects in official correspondence sanctioning the deportations.

With the briefest of nods to Robin Cook’s supposedly ethical foreign policy, the British government initially agreed to readmit them to the Chagos archipelago, a dependency hived off from Mauritius in the 1960s after Washington earmarked its largest atoll, Diego Garcia, as an ideal military base. The promise was empty, however, and promptly slapped down by the Queen, using an arcane prerogative that harks back to pre-Magna Carta days of absolute monarchy.

Such abuse of power is unparalleled, even in Britain’s long legacy of imperial crimes, argues the Chagossians’ barrister, Sir Sydney Kentridge, who in the past defended Nelson Mandela and Steve Biko in their struggles against apartheid.

“There is no precedent that we have been able to find in statute, case law, or indeed in history for what has been done,” he told the two judges presiding over the High Court. “The matter has never been placed before the UK parliament.”

Presumably because it would have been thrown out, and with good reason. So just how did the Chagossians come to be denied the most basic of human rights in a decision that makes a mockery of British democracy? The answer remains shrouded in secrecy, but declassified documents shed some light on what probably went on.

After a U.S. Navy Rear-Admiral first set foot on Diego Garcia in 1961, the question preoccupying Washington and Whitehall in secret was how to effect the “cleansing” and “sanitising” of the Chagos islands without attracting worldwide condemnation.

A 1965 Foreign Office memo describes how the United States made the depopulation of the archipelago “virtually a condition of the agreement” to lease it from Britain, ostensibly fearing for the security of what was to become one of the Western alliance’s most treasured bases. In return for promising to “make up the rules as we go along”, Harold Wilson’s Labour government was rewarded with an $11 million discount on an American nuclear weapons system that it had previously pledged not to buy.

To justify the decision that there would be “no indigenous population except seagulls” after transporting the Chagossians 1,000 miles to Mauritius and the Seychelles, British officials invented “whopping fibs” to “maintain the pretence that there were no permanent inhabitants” on the islands.

The rationale for concocting these lies was clear. “We could not accept the principles governing our otherwise universal behaviour in our dependent territories,” one briefing paper stressed. “When a particular island would be needed for the construction of … defence facilities, Britain or the United States should be able to clear it of its current population.”

It remains unclear whether Washington has designs on other islands than Diego Garcia, since all were emptied and declared off-limits to their former residents. Although that ban was nominally lifted in 2000, the U.S. warned this was a “threat to national security” and nobody was so much as granted permission to visit before the Queen exercised her prerogative to intervene with an Order in Council.

In Parliament last year, the Scottish National Party leader Alex Salmond asked Tony Blair whether the right of return had been revoked because Washington was intent on keeping Diego Garcia, “perhaps to use it as another Guantanamo Bay?”

There was “no question” of any such thing, the Prime Minister insisted. Twelve months later, Amnesty International told a U.S. Senate hearing it had evidence that the island was part of a network of secret CIA prisons, where “detainees are being held arbitrarily, incommunicado and indefinitely without visits by the Red Cross.”

Camp Justice, as the U.S. calls its base, also plays host to feral donkeys and chickens abandoned by the islanders, in addition to 3,500 military personnel, a satellite spy station and warplanes used to bomb Iraq and Afghanistan.

The Chagossians have abandoned hope of returning to Diego Garcia itself. Whether or not they can resettle the neighbouring atolls will be resolved by a debate about the use of the same royal powers that helped ignite the American Revolutionary War. Will justice prevail over Britain’s allegiance to the whims of the Pentagon? History suggests not.