The Spanish estate agent acting for the self-proclaimed nation has also declared that Piratebay may not be allowed to buy it because it has pledged not to allow a sale that would damage the interests of or act against the UK.
Piratebay has been the focus of a burgeoning political movement in Sweden. The server farm hosting the site was raided last year causing popular outcry in a country where file sharing is significantly more socially acceptable than in other European nations. The site provides links to material that is often downloadable without a licence or permission.
Piratebay has said that it now wants to find a location where it can set itself up as a nation and avoid copyright laws, and has said that it has started negotiations with the family that has long claimed Sealand as a sovereign nation.
But Professor Robin Churchill, a lecturer in constitutional and international law at Dundee University, says that Sealand's 1967 claim to sovereignty is absurd. "It is within 12 miles of the coast of Britain and in 1987 the UK extended its territorial waters to 12 miles. That means that UK law applies, including the law of copyright, which could be extended to Sealand without any legal problems whatsoever," he said.
The man behind Sealand, former major in the British army Paddy Roy Bates, has long claimed that his 1967 declaration of sovereignty predates that extension, and therefore supercedes it.
"That is complete nonsense," said Churchill. "For it to be a state a place needs to have a proper stable population, a functioning government and needs to be recognised by other states and no existing other state recognises Sealand."
"Like all island countries, the Principality has actively sought inward investment," said a Sealand statement announcing its sale. "We have now secured the services of a Spanish property broker who will act on our behalf to seek significant inward investment here in the Principality by way of either purchase or long-term lease."
The Spanish estate agent acting for Sealand in the sale says that it cannot be sold as such because its occupiers claim that it is a principality. The transfer fee, though, is set at £504,000.
The team behind Piratebay has expressed its interest. "We want to buy Sealand. Donate money and you will become a citizien," said a statement on Buysealand.com, a Piratebay website. "The Government of Sealand has initiated negotiation. Tomorrow, the ACFI [Piratebay] and Government of Sealand will sit down to discuss the future of the micronation."
Piratebay has asked for donations to fund its purchase, but that money could be wasted if Churchill's view of the structure's legal status is correct. "There is nothing in international law to stop the UK enforcing its law there," he said.
The estate agent, InmoNaranja, has said that Piratebay may not be allowed to buy Sealand. "We might not be able to sell to them, since one of the conditions imposed by the actual occupants of Sealand is that none of the activities to be carried out on Sealand should be an action against the UK, and potentially this group does not comply with this condition," said a statement from InmoNaranja. "The final decision lies with the current representatives of Sealand at the time of seeing the purchaser's proposal."
Bates has always claimed that a 1968 English court judgment which said that it had no jurisdiction over the ex-anti aircraft installation validated its claims for legitimacy and international recognition. He also argues that contact with Sealand made by a German diplomat over the holding of a German national on the installation constituted diplomatic recognition of its nation status. Legal experts, though, have argued that those incidents are unlikely to be enough to justify the declaration of nationhood which Bates and his family claim.
Piratebay has said that if it fails to buy Sealand it will buy a very small island instead and attempt to assert nationhood there. It says prices for islands start at around $50,000.