The French Government tried to blame the 1985 sinking of the Rainbow Warrior on the British secret service.

The Times newspaper in London has reported that documents released under the Freedom of Information Act show Prime Minister Margaret Thatcher was infuriated by the campaign of "misinformation and smears" suggesting that MI6 bombed the Greenpeace flagship in Auckland and framed French secret agents, or that MI6 knew in advance of the mission.

Sir Malcolm Rifkind, then a Foreign Office minister, told UK diplomats in Paris to demand an end to media reports, but they continued to appear.

Sir John Fretwell, the British Ambassador in Paris, wrote of French officials' "desperate attempts to find answers which will somehow satisfy public opinion while keeping the then President, Francois Mitterrand, above the controversy".

Sir John privately warned the British Government that President Mitterrand could be forced to resign in a Watergate-style scandal, the Guardian newspaper reported.

The July 11, 1985, bombing, which killed Greenpeace photographer Fernando Pereira, was carried out by French agents, including Alain Mafart and Dominique Prieur, who were arrested in less than a week.

But during July, French journalists reported a theory that MI6 had sunk the Rainbow Warrior to discredit France and had then framed its secret agents, the Guardian reported.

In other versions French media claimed that French secret agents had bought the dinghies used to plant the bombs from people close to MI6 and that MI6 knew of the planned sabotage.

By late August the Sunday Times was telling the Foreign Office that "French official sources were briefing freely to 'anyone who would listen' about British involvement".

The British Government traditionally never comments on anything to do with MI6, but off the record told reporters that the stories were "pure fantasy". Whitehall suspected the "mischievous" French Embassy in London was spreading the stories, though the French denied everything.

On September 4 a Foreign Office official wrote: "Despite all these protestations of innocence, the cumulative evidence ... of French official briefing now seems irrefutable".

President Mitterrand clung on and it only emerged this year that he had authorised the bombing. Mafart and Prieur pleaded guilty to manslaughter in November 1985 and were sentenced to 10 years' jail.