A lengthy legal battle over the rights to treasure believed to be worth £1bn, which went down with a Spanish galleon 300 years ago off Colombia's Caribbean coast, was thrown into further confusion yesterday despite a ruling by Colombia's highest court to finally decide ownership.

The gold, silver and jewels on board the San José, which sank on June 8 1708 while trying to outrun British warships near the port of Cartagena, make it one of the world's most valuable shipwrecks. The treasure has been the focus of a legal battle between the Colombian government and American salvagers.

The supreme court ruled yesterday that Colombia holds the rights to items deemed to be "national cultural patrimony". Anything else will be halved between the US salvage company Sea Search Armada and Colombia.

The ruling, which cannot be appealed against, overturned two earlier court decisions that awarded Sea Search half of the haul. But a Colombian lawyer for Sea Search Armada still claimed victory.

"We are satisfied with the ruling," said Danilo Devis, who said most of the cargo would not be considered Colombian patrimony, since the San José was a Spanish ship coming from Peru. "If anything it's Peru's cultural patrimony."

But Martín Andrade, of Colombia's culture ministry, said: "It is all Colombian cultural patrimony because it is in Colombian territory." If that broader interpretation of cultural patrimony is upheld, Mr Andrade acknowledged that the court decision may leave little incentive for Sea Search, or any other wreck salvagers to dive for the San José or more than 1,000 other wrecks believed to lie off Colombia's Caribbean coast.

In 1979, Sea Search Armada, along with 100 US investors, signed a deal with Bogotá giving them exclusive rights to search for the San José and to keep half of whatever they find.

What is believed to be the wreck of the San José was found 700ft (200 metres) below the surface in 1982 by the Glocca Morra Company, which sold its rights to Sea Search. Colombia's General Maritime and Port Authority recognised Sea Search's right to half of what may be found. But two years later President Belisario Betancourt issued a decree slashing Sea Search's rights to 5% of the treasure.

In 1994 a judge in Barranquilla ruled in favour of Sea Search, upholding the 50/50 deal. Three years later an appeals court again upheld the ruling. Now, if the treasure is raised, ownership of each item will probably have to be decided by independent experts.

Even throughout the court battles, some doubt has emerged as to whether the ship has even been found.

A treasure hunter hired by the government to verify the coordinates turned up nothing. An underwater video taken of the alleged wreck in 1982 shows what looks like a coral reef-covered woodpile.

The San José was part of Spain's only royal convoy to try to bring colonial bullion home to King Philip V during the war of Spanish succession with England from 1701-1714.

All 600 crew members were believed to have died in the wreck.

More treasure

HMS Sussex In 2002, US treasure seekers found the wreck near Gibraltar. It contained £2.4bn in gold and silver. In March they reached a deal to split profits with the UK, and took coins worth £250m to the US.

Merchant Royal The same treasure seeking firm, Odyssey, won rights over the 17th-century ship at a US court this year. Odyssey says the vessel lies "100 metres beyond territorial waters" off Cornwall.

Rooswijk 18th-century wreck found by a diver in 2004 off Kent. Silver worth £450,000 was handed to the Netherlands, the ship's owners.

HMS Fantome The ship sank off Canada, reportedly carrying valuables looted from the White House and US Treasury during the War of 1812. The UK claims ownership but the wreck lies in Nova Scotia waters.

Katy Heslop