The minute outcrop of rock, which measures just 110 feet in diameter and rises to a peak of 65 feet, lies almost 300 miles off the western coast of Scotland at the centre of rich, developing oil fields in the Atlantic.
The campaigners, two men and a woman, were winched down from a helicopter on to the exposed rock on Tuesday evening, their actions a protest at extended oil exploration in the area. The trio, named as Al, Peter, and Meike, have been bolted to Rockall in a 12 foot by 6 foot survival capsule and have stated their intention of remaining there indefinitely.
A spokesman for Greenpeace said: "We have asked the UK government to stop oil exploration in the Atlantic Frontier region and when they do they can have their rock back."
Al, 32, a protester from Newhaven, Sussex, added: "By seizing Rockall we claim her seas for the planet and all its peoples. No one has the right to unleash this oil into our threatened climate."
The trio are unlikely to suffer the same fate as fellow eco-warriors, such as those at Manchester Airport, and be prised from the rock. Yesterday the Government said that it has no intention of evicting the three from their new abode.
A spokesman for the Foreign Office told The Independent: "Rockall is British territory. It is part of Scotland and anyone is free to go there and can stay as long as they please."
Nigel Scott, of Western Isles Council, who since 1975 have had jurisdiction over Rockall, said: "There is no obvious reason why we would feel obliged to interfere in what is happening. We have no powers to forcibly remove them and they do have rights to be there."
In another twist to coincide with the "invasion" of Rockall, Greenpeace warned Margaret Beckett, President of the Board of Trade, that unless she acted over their claims that the Government ignored EU directives protecting the area's marine eco-system, they would seek a judicial review from the High Court. A DTI spokesman said: "If Greenpeace take court action we will deal with that."
Rockall has long been a source of territorial tensions between Britain, Ireland, Iceland and Denmark. Britain seized the hunk of volcanic rock in 1955 when Royal Marines planted the Union flag on the island. Before the arrival of the Greenpeace activists it has been uninhabited, save for the stay of a former SAS soldier, Tom McClean, who camped for 39 days on the rock. Britain is anxious to retain ownership, particularly since surveys have discovered valuable oil deposits in the Foinaven and Schiehallian fields close to the rock.
Under the 1982 Law of the Sea Convention, waters surrounding islands are the property of the controlling nation, but if the land mass is deemed uninhabitable and economically non-practicable, the land is defined as a rock and no control of nearby waters exists.
However Britain is not a signatory to this law. During recent years other countries have questioned the British definition and raised tensions in the area. In 1992 two Irish brothers tried unsuccessfully to land on the rock and paint the Irish Tricolour on it while in 1994 a Cypriot vessel with an Icelandic skipper was arrested by a Scottish Fisheries Protection vessel.
1. Celtic legend says Rockall is the last remnant of Brasil, the Western Land of Eternal Youth submerged by the Atlantic.
2. During World War I the rock was mistaken for the conning tower of a German U-Boat.
3. In a Commons debate in 1971, Mr William Ross, MP for Kilmarnock, said: "More people have landed on the moon than have landed on Rockall."
4. In 1904 a Danish ship, Norge, was wrecked off the island with the loss of 600 lives.
5. During the Cold War, Rockall was viewed as a security risk. It was feared the Soviet Union would monitor missile tests from there.
6. Rockall is one of the 31 areas made famous by Radio 4's shipping forecast.
7. In 1971, Lord Kennet said: "There can be no place more desolate, despairing and awful."
8. Rockall was annexed by troops from HMS Vidal in 1955 as part of the preparations for a guided weapons training range.
9. In 1969, it was said that Rockall lay over an extinct volcano that erupted 50 million years earlier.
10. In 1955, Scotsman J Abrach Mackay claimed Rockall for his family. He said: "My old father claimed that island for the Clan Mackay in 1846 and I now demand that the Admiralty hand it back. It's no' theirs."