Access to the platform is only possible by helicopter or boat
For 30 years an eccentric ex-Army major's claims that a gun platform off the Essex coast is an independent state have been ignored by the government.
But documents just declassified by the National Archives show that at one time the "world's smallest state" was such an embarrassment officials wanted to bomb it into the sea.
To the British government Roy Bates must have seemed like an insolent child sticking two fingers up from just out of reach behind a garden wall.
In 1967 the former Army major took over a World War II fortress seven miles off the Essex coast and declared it an independent state, with himself as monarch.
Standing just outside British waters (which until 1987 only stretched to three miles), the government was powerless to remove him, and there he stayed for nearly 40 years.
Mr Bates and his 'Principality of Sealand' came to be treated with the special indulgence reserved for English eccentrics; but just declassified documents show that at one time the peculiar story was close to taking an altogether darker turn.
The papers reveal a diplomatic row with Germany and Foreign Office officials, who were so incensed that they called for the Navy to knock the 10,000 sq ft platform into the sea.
The trouble began in August 1978 when two Germans and a Dutchman landed by helicopter on the platform, overpowered Mr Bates's son, and laid claim to the "principality".
The victory was short-lived. Soon afterwards the major staged a "counter-coup", freed his son and took the Dutchman and one of the Germans hostage.
It was not long before the Dutch and German embassies contacted the Foreign Office, asking when their citizens would be released from British captivity.
The German Embassy wrote stiffly: "The German national Gernot Ernst Putz is being held prisoner by members of a so-called 'Principality of Sealand' on the former anti-aircraft fort 'Roughs Tower', off Harwich.
"Therefore, the imprisonment of Putz is in a way an act of piracy, committed on the high sea but still in front of British territory by British citizens."
The trouble was that as Sealand lay outside British jurisdiction there was nothing the Foreign Office could do.
The embarrassment of being powerless to control the antics taking place on a concrete stack within sight of the British coastline was, it seems, the last straw.
'Strident' and 'petulant'
In a classified internal letter following the Dutch entreaties, a Foreign Office official wrote: "Could you, therefore, please discuss the approach from the Dutch embassy with the Whitehall departments concerned, and let me know what reply I can give to Mr Schaapveld?
"Is there any chance of a British patrol vessel 'passing by' the Fort and somehow knocking it into the sea?"
Before he could receive a reply, the Dutch hostage was released. But it appears this latest humiliation was a step too far and the official felt Mr Bates had to be dealt with once and for all.
He wrote: "Mr Schaapveld said he did not know whether the German… had also been released. Assuming that he has, then we can consider the problems of Sealand in somewhat slower time.
"But no doubt the same sort of problem might be thrown up at any moment until the British government feels itself able to take some effective action over its property in the North Sea."
Sealand is seven miles from the coast of England
As it turned out the German hostage had not been released. Instead the Foreign Office received further "strident" and "petulant" demands from the German embassy.
It was not long until the man was set free, but by now the Sealand question had gained its own momentum and the issue was raised as a parliamentary question in the House of Lords.
Lord Kennet asked: "My Lords, is it not the case that the British national on this tower has been reported in the press as having taken actions which, if they had been committed in a place where there was jurisdiction, would have been crimes, but that as there is no jurisdiction on this tower no action has been taken to restrain him from capturing or kidnapping people and holding them to ransom?"
Lord Goronwy-Roberts replied: "My Lords, I think that the noble Lord puts the position fairly."
Lord Hailsham of Saint Mary-Lebone said: "Quite seriously, my Lords, is not such an instillation a danger to navigation and, so many years after the war, is it not time that it was sunk or demolished in some other way?"
Lord Goronwy-Roberts said all options were being considered, including demolition.
The National Archives file holds a final letter from a Foreign Office official noting that the MoD had a plan for re-capturing the tower "if, and when, it became apparent that the Bates family were no longer in residence".
The official asks "whether the MoD is still ready to take action if required and also what sort of action would be taken".
There is no reply contained in the file, but Sealand was not demolished by the Navy and is still standing, still occupied and still unrecognised by the government.
In 2007 the Bates family put "their" nation up for sale. A Spanish estate agents specialising in selling islands gave it a price tag of £504m.