Phil Wells - known as 'Florida Phil' - 48, a father- of-two, of Hounslow, west London, will be sentenced next month.
Wells denied stealing pounds 928,000 in foreign currency but admitted having a false passport and driving licence. He was arrested earlier this year trying to sell his story to a national newspaper.
Judge David Miller warned him: 'It must be obvious to you as well as to everyone else that you have been convicted of a very serious offence and there is bound to be a lengthy custodial sentence.'
The money was taken while Wells worked as a pounds 2.50-an- hour guard for an Ealing security firm in July 1989. He was due to deliver nine bags from a Portugese aircraft to a strongroom for later despatch to Thomas Cook. But, following the collection, he disappeared. His Ford Escort van was found two days later but he deceived police by telling a relative he was heading for Florida while he was hiding in a caravan in Clacton. He later stayed at Butlins in Great Yarmouth and in hotels in Folkestone before going abroad.
None of the stolen cash has been recovered. Wells claimed he never received more than pounds 30,000 and had only taken part in the robbery under duress.
An earlier visit to Florida, during which he married his second wife and spent a pounds 20,000 inheritance and pounds 7,000 redundancy pay, was said to have inspired a taste for the high life.
Detectives said he would have needed a considerable amount of money to maintain his lifestyle.
When arrested, he told police of numerous countries he had visited while on the run, a stroke he had suffered in Paris, and his marriage to Olga, his third wife, who still lives in Malta, where he spent much of his time.
Wells met Olga, a teenage gymnast, in Yugoslavia and they were married in her home town of Tashkent, in the former Soviet state of Uzbekistan in June 1991. She believed him to be Ronald Hill, a wealthy greengrocer with shops in Essex.
In court, Wells told the jury of six men and six women how criminals from the East End of London had issued death threats against him and his two sons to make him follow their orders.
The 'main man' behind the operation was said to be a greengrocer who used to be his landlord and who was acquitted of handling pounds 100,000 of the money earlier this year.
Gino Connor, for the prosecution, said in court that Wells had undoubtedly 'fallen among thieves' but had willingly took part in the theft.
Even if he was put under some pressure at some stage he had ample opportunity to pull out, he added.
Three other men were detained at the time of Wells's arrest and have been charged in connection with events on the night of the robbery.
Detective Inspector Norman Walker said after the case that investigations into the theft have not ended.
'Following his arrest, several lines of inquiry have been opened and are still being pursued,' he said.
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