A few springs ago David MacMillan came home from his shift at Inverness hospital and tried to open the front door of his semi-detached council house. He could not. It was jammed with A4 envelopes wrapped in cellophane.

The auxiliary nurse laughs at the memory. "After I eventually forced myself in, I counted the letters," he says before leaving a long pause. "There were 485 in just one day."

Mr MacMillan, a 41-year-old father of one, gets a lot of mail. Or rather his home does. Because it is the official address of - at last count - around 600 Scottish limited partnerships, or SLPs, the once obscure kind of firm which anti-corruption body Transparency International calls the "UK's home-grown secrecy vehicle" because, until very recently its true owners could be legally secret.

Among the firms registered at his home, in Merkinch, were five used as part world's biggest bank heists - the systematic looting of $1bn from three financial institutions in the former Soviet republic of Moldova.

Now, again thanks to The Herald, Mr MacMillan had just discovered that his house was also the registered address of the owner and operating of a ship currently abandoned in Istanbul after it was used to break international sanctions on trade with Russian-occupied Crimea. "Oh God', he says.

Mr MacMillan sees funny side, the sheer absurdity of his near-accidental role as a mailbox for global skullduggery. But he was so sanguine when law enforcement first noticed his house on Rosehaugh Road.

"They fraud squad came," he says and blows out a long, whistling sigh as he gathers his thought. "I mean, the fraud squad at my door. I am a pretty laid-back guy. I don't get stressed but I just lost it. It was scary.

"I am an average guy from Inverness who works in his local hospital on a zero-hours contract. I am definitely not a gangster or anything like that.

"I am a guy who goes about his business and does not say boo to a goose so there is no way I have anything to do with all these criminal activities."

So how did an Inverness council tenant - earning less than £20,000 a year - end up as a front for a £1bn bank heist and an embargo-busting ship?

Mr MacMillan used to share his home with a partner, a Latvian called Liene Brice. She also has nothing, he says, to do with crime. He explains "Years ago my ex got an email from a former schoolmate looking people in the UK to help with processing letters. She said she would give us a scanner and we could scan letters that came in. We agreed, telling them to send the money to my then partner's mother in Latvia."

Then the letters, sometimes scores a day, 500 a week. For a while, Ms Brice scanned them. Then the police came. "They told me we were dealing with fraud and I could not believe it. We tried to help her mum to find out we were actually helping other people without knowing." Now, years later, with his girlfriend gone and her friend's associates told not to send any, MacMillan simply gathered all the letters in to a bag and gives them to the authorities. Police Scotland, "down south", he says, have a close interest.

Mr MacMillan is not the only Scot who has found himself as the unlikely host of hundreds of firms. many involved in criminal or unethical conduct. There are 30,000 SLPs registered in Scotland, the vast majority with untraceable real owners and based, theoretically, at everything from local photo-copying shops to council flats. Under new rules imposed this month they have, in theory, to name their 'person of significant control' or face daily fines of £500 until they do so.