A top judge has taken the unprecedented step of ordering two senior Government officials to face cross-examination in court over a classified US document leaked by WikiLeaks.
Despite strong objections from lawyers acting for Foreign Secretary William Hague, the High Court judge ruled today the move was necessary to resolve "fairly and justly" a claim launched against the Government by exiled residents of the Chagos Islands.
The judge declared the leaked US cable - alleged to relate to a private US-UK diplomatic meeting - could be investigated in court even though it must have been obtained unlawfully by "the notorious internet organisation".
The groundbreaking ruling will come as a blow in Whitehall, which argued the courts should not entertain any applications for cross-examination in relation to documents unlawfully obtained by WikiLeaks.
The British expelled the Chagos islanders between 1965 and 1973 in order to allow the US to establish an airbase on Diego Garcia, the largest island in the Chagos archipelago in the British Indian Ocean Territory (BIOT).
The expulsion has been described by critics as one of the most shameful episodes of modern colonial history.
The islanders have been fighting a long campaign, which has included a string of court cases, for the right to return to at least some of the islands.
Today's hearing relates to a new High Court application by the Chagos Refugees Group for judicial review of the Government's decision to create a Marine Protected Area (MPA) round the islands.
Commercial fishing is banned within the MPA. The islanders say the MPA was created for the "improper purpose" of preventing resettlement of the islands.
The UK Government denies anything improper and maintains the MPA was created for environmental reasons.
But the islanders say their case is supported by the cable obtained by WikiLeaks. It was sent by the US embassy in London to the US State Department in Washington in May 2009.
The MPA was established in 2010 by a proclamation made by Colin Roberts, Commissioner for the BIOT, acting upon the directions of the British government.
The court heard that, in the leaked cable, Mr Roberts asserted at the May 2009 diplomatic meeting with the Americans that creating the MPA would not adversely affect US defence interests - but it would the islanders.
Mr Roberts is reported in the cable to have asserted "establishing a marine park would, in effect, put paid to resettlement claims of the (Chagos) archipelago's former residents."
Nigel Pleming QC applied on behalf of the Chagossians earlier this month for permission to cross-examine Mr Roberts when the Chagossian judicial review application comes on for hearing in the near future.
He also applied for permission to cross-examine Joanne Yeadon, a civil servant at the Foreign and Commonwealth Office at the talks with the Americans.
Mr Pleming said it was not suggested that the WikiLeaks cable was not a genuine document, but the Government was hiding behind a "neither confirm nor deny" policy.
Mr Pleming said he wished to question Mr Roberts in the witness box about his discussions with his US counterparts and to test the denial that an improper motive drove the creation of an MPA.
Steven Kovats QC, appearing for the Government, said the High Court was in "a novel situation" with regard to WikiLeaks disclosures.
Mr Kovats said: "My clients are not opposing cross-examination because they have anything to hide.
"We are opposing it because, as a matter of principle, it does not seem right in relation to an improperly leaked document.
"We, as a matter of principle, do not accept that WikiLeaks can effectively compel the Government to defend something which - absent WikiLeaks - there would be no question of it coming before the court at all."
Today Mr Justice Stanley Burnton rejected the Government's objections and ordered that cross-examination should go ahead.
The judge said he acknowledged that the US document "must have been obtained unlawfully, and in all probability by the commission of a criminal offence or offences under the law of the United States of America".
He added: "I understand why it is the policy of HM Government neither to confirm nor deny the genuineness of leaked documents, save in exceptional circumstances, particularly where, as here, the documents in question are not those produced or received by the UK Government.
"However, the documents have been leaked and indeed widely published."
No application had been made for a public interest immunity certificate to prevent the courts openly investigating the genuineness of the cable.
He ruled: "I do not see how the present claim can be fairly or justly determined without resolving the allegation made by the claimant, based on the WikiLeaks documents, as to what transpired at the meeting of 12 May 2009, and more widely whether at least one of the motives for the creation of the MPA was the desire to prevent resettlement.
"Given the conflicting evidence, in my judgment, in order to resolve the dispute, oral evidence will be necessary, including cross-examination of Mr Roberts and Ms Yeadon."