Mr Fossett went missing last September after taking off from a remote Nevada airstrip on a short trip to inspect a site for possible use in a land speed record attempt. He never returned. His disappearance sparked the most intensive hunt for a missing aircraft in US history, involving Civil Air Patrol's Black Hawks fitted with infra-red technology, as well as 30 private aircraft and a global internet effort led by Amazon.com and Google.

Mrs Fossett contributed over $1m to the efforts, her lawyers have said. Neither Mr Fossett's body nor the plane's wreckage were ever located.

But Lieutenant Colonel Cynthia Ryan, of the US Civil Air Patrol, who briefed the media during the search, has said the adventurer's body 'should have been found', given the extensive search efforts, suggesting he could still be alive.

'It's not like we didn't have our eyes open. We found six other planes while we were looking for him. We're pretty good at what we do,' said Lt Col Ryan, who added she believed Mr Fossett may have faked his own death due to personal problems or fears about his business dealings.

Mr Fossett made millions trading futures and options on Chicago exchanges.

Risk assessor Robert Davis, who conducted an eight-month investigation for insurers Lloyd's of London, said he had 'discovered that there is absolutely no proof that Steve Fossett is actually dead'. Lloyd's is said to face a £25m payout on Fossett's death.