The government is refusing to admit that thousands of classified US embassy cables obtained by WikiLeaks and published in the Guardian are genuine, the high court has been told.

It was made clear that the refusal was intended to protect the government from the charge that it imposed a Marine Protected Area around the Chagos Islands in the British Indian Ocean Territory (BIOT) to prevent the islanders from ever returning to their homeland.

Lawyers representing the government made it clear that it was also worried about upsetting the US if it confirmed that the leaked cables were genuine.

A US embassy cable published in the Guardian in December 2010 quoted a senior Foreign Office official, Colin Roberts, telling the Americans that as a result of imposing the marine reserve, there would be no "human footprints" or "Man Fridays" on the islands.

He said the plan would "in effect, put paid to resettlement claims of the archipelago's former residents", according to the cable.

The case is the first resulting from the leak of classified US cables in which UK officials have been ordered to appear.

Roberts, commissioner of the BIOT at the time of his meeting with US officials in May 2009, will take up a new post next year as governor of the Falkland Islands, the high court heard on Monday.

Steven Kovats QC, for the Foreign Office, said the government would stick to a policy of "neither confirm nor deny" over the authenticity of the documents. The policy is known in Whitehall as NCND.

There were concerns about the "repercussions for the relations between HMG [Her Majesty's government] and the US" , Kovats said.

If that US embassy cable was authenticated, people would call for other cables to be admitted, Kovats told Lord Justice Richards and Mr Justice Mitting.

There was a "real distinction" between a document and information, he said. Kovats said Nigel Pleming QC, counsel for a group of Chagos islanders, could question Roberts about his meeting with US officials in May 2009 and newspaper articles referring to it, but not about the contents of the leaked cable.

Questioned by Pleming, Roberts denied he had said the marine reserve idea was a plan with an "ulterior motive" – namely, to prevent the islanders from returning.

Pleming is representing Louis Bancoult, chairman of the Chagos Refugees Group, who has seized on the leaked cable to argue in the British courts that the decision to impose a marine reserve announced by the then foreign secretary, David Miliband, in 2010, should be declared unlawful.

The inhabitants of the archipelago were removed in the 1960s and 1970s when the UK agreed that the US could build a large military base on the largest island, Diego Garcia.

That decision, and the subsequent decision to impose a marine reserve area, will have to be justified before an international tribunal.

In an unexpected ruling earlier this year the permanent court of arbitration in The Hague ruled that Britain would have to justify its decision before a full hearing of the tribunal. An attempt by the UK to challenge the court's jurisdiction was defeated.

The Mauritian prime minister, Navinchandra Ramgoolam, has said the decision to establish a 545,000 sq mile marine reserve was carried out in defiance of assurances given to him at the time by the then prime minister, Gordon Brown.

The BIOT was established in 1965 when Britain expelled the Chagos islanders and allowed the US to set up a large base in a deal that included cutting the cost of Polaris missiles for the UK's nuclear submarines.

The agreement signed by the US and UK in 1966 expires in 2016. Both parties must agree to extend, modify or end it by December 2014. Ramgoolam told the Guardian last year that the objective of Mauritius was to "reassert sovereignty" over the Chagos islands.