Britain abandoned bid to recover lost £5.5bn treasure from a Royal Navy shipwreck near Gibraltar in case it upset Spain

Britain abandoned its fight to recover treasure worth £5.5billion from a Royal navy shipwreck near Gibraltar over fears it would upset Spain.

Leaked cables from the early 2000s show how ministers scrapped plans to rescue a warship understood to be HMS Sussex in case it would threaten relations with Spain, despite the UK owning the wreck. 

HMS Sussex was a Royal Navy flagship lost off Gibraltar more than three centuries ago. It is believed the wreck sits in international waters to the east of Gibraltar, which Britain could claim under international maritime law. 

The warship sunk in a storm in 1694 while carrying up to 10 tons of gold, records suggested, which would amount to £5.5billion today - making it the most lucrative shipwreck discovered.

In 2001, Odyssey Marine Exploration, the US deep sea exploration company, said it was '99 per cent' sure it had found the ship after a three-year search.

The UK government signed an agreement with the company in September 2002, agreeing to recover the wreck and for the sale of treasure to be split. 

News of the contract sparked furore and incited diplomatic tensions with Spain, which said it owned the ship due to its position in claimed Spanish waters. 

It emerged through once confidential diplomatic cables from the US that UK officials said the dispute was causing 'an unnecessary threat' to British-Spanish relations.

In the documents, released by Wikileaks, Dame Denise Holt, then deputy head of mission at the British embassy in Madrid, said officials would seek to 'terminate' the contract with Odyssey. 

She added in June 2007 the 'controversy' made the British embassy 'distance themselves as much as possible from Odyssey', and was also impacting 'Gibraltar issues'. 

The Florida-based Odyssey would also, she said, lose British 'aid' when their ships sailed from the port of Gibraltar, where they were moored.

Meanwhile Carmen Calvo, Spain's culture minister, said in a separate cable dated November 2005 that Odyssey would look for HMS Sussex 'over her dead body'. 

In the leaked correspondence, the Odyssey was described as a 'six year saga'.  

The wreck was discovered 821 metres (2,694 feet) under the Mediterranean sea in 1998, and identified using underwater robots and remote operated vehicles. 

The mission was said to have cost Odyssey millions of dollars, while the project's team were 'hounded' by 'aggressive' Spanish patrol boats.

Neil Cunningham Dobson, a marine archaeologist on the project, told the Daily Mail: 'The Guardia Civil were hostile towards us. We had to abandon the site, leaving equipment and archaeological investigations not completed.' 

'They were aggressive towards us,' he added. 

The deal between the UK government and the company allowed Odyssey to claim 80 per cent of the first $45million (£33million) made from selling the coins. 

Any proceeds then up to $500million (£375million) would then be split equally. The rest would be split 60-40 between the UK and Odyssey.

Spain said it held a claim to Gibraltar and added the ship could have been one of its own, despite a lack of evidence behind this. 

However, international law gives UK authorities jurisdiction over the wrecks of British ships wherever they may lie.  

The project then halted while the contract Odyssey ran its course. It was reported Spain sent out coastal patrols in attempts to disrupt the operation. 

The ship was on a secret mission taking gold and silver coins to the Duke of Savoy to help finance his war against Louis XIV in the Nine Years War against France. 

It was the flagship for Admiral Sir Francis Wheeler's fleet of 40 warships and 166 merchant ships. 

Only two people out of the 550 crew survived, it is believed. The admiral's body was washed up on a Spanish beach two days later. 

The Ministry of Defence and Odyssey have been contacted for comment.