More than 300 firearms, including Israeli Uzi submachine guns and pump-action shotguns, were found in Michael Lee's house in Teignmouth after a police raid in 2001.
Lee, a crane driver who was then 56, also had 25,000 pieces of live ammunition in the house.
The disclosure that he has tens of thousands of pounds in an offshore bank account despite living in a modest suburban home in a seaside resort is expected to lead to renewed questions over his activities. Lee claimed when prosecuted to simply have a fascination with guns.
Last night, it was not clear why HSBC agreed to open an account for Lee or whether British authorities had been alerted to his offshore windfall previously.
The pensioner was jailed for two years for firearms offences in 2002. His wife, Caroline, who was unemployed, was given a 12-month conditional discharge when she admitted one charge of possessing a prohibited weapon.
At the time, Detective Sergeant Ken Lamont said: "Whatever the circumstances of the acquisition of the firearms, the danger they pose to society is such, especially with the amount of ammunition involved, that such a sentence had to be imposed."
Approximately 140 of the weapons were securely held in various safes around the house while the others were stored behind fitted units.
The cache of weapons had cost around £25,000 to acquire.
At the time, the police said there was nothing to suggest a connection to terrorist activity. It was the largest-ever seizure of guns and ammunition from one person made by Devon and Cornwall Police.
Lee claimed to be "fascinated" by guns and was told by Judge William Taylor that he had an "unhealthy obsession" in relation to guns and ammunition.
At the time, the police said Lee had collected the weapons over a lifetime from private sales; registered dealers when they were lawfully able to trade in them, and by word of mouth. The collection included a 12-bore shotgun, handguns, an M16 assault rifle and a WW2 Bren gun. Lee's shotgun certificate was cancelled.
The couple bought their house on a quiet street in the seaside resort of Teignmouth for £133,000 in 2001.
The modern house, which is surrounded by wooden fences and tall conifer bushes, has a panoramic view of the town and the surrounding countryside.
Yesterday, neighbours said the couple "kept themselves to themselves".
The house was quiet and there was a silver people carrier car parked in the corner of the drive.
One neighbour confirmed the couple lived at the address.
"I know their names but that is about all. They keep themselves to themselves and I don't know anything about them really. I don't know if they work or if they are retired."
Another neighbour said: "I don't know the people who live there at all. I couldn't tell you their names or anything."
The Lees are one of several people with criminal records understood to be on a list of account-holders obtained by HM Revenue and Customs.
Uzi submachine guns are capable of firing at extremely high speed. They have been nicknamed the "spray and pray" amongst the criminal fraternity.
Computer thefts: Criminal deposited £100,000
A man once labelled London's "number two computer crook" is understood to have more than £100,000 in an HSBC account in Jersey.
Misha Elias, now 52, from north London, was at the "forefront of a major network of people" burgling offices and stealing computers. After a trial at Middlesex Guildhall court in 1998, Elias was sentenced to two years in prison. He was ordered to pay costs of £25,000 plus a confiscation order of £120,000, or serve an extra three-year sentence. It is not known if the money was ever repaid but Elias now lives in a modest flat and describes himself as a "publishing consultant". His co-defendant in the case, Charles Davis, reportedly deposited more than £770,000 in various bank accounts in his wife's name in London, France and New York while trading in the stolen computers.