Ascam e-mail pops into your inbox. What do you do? You know the type, invariably written in broken English, with a veneer of respectability: “Dear Sir/Madam, how are you this fine day? I write on behalf of my client, God help her, whose husband has died tragically. She needs to move £20 million quickly to the UK to protect his estate for her children. If you allow us to transfer the sum into your bank account, you will earn 10 per cent as our foreign partner. Peace be with you.”

Do you feel a flush of irritation, then hit the delete button? Perhaps you feel slightly smug that you’re not one of those dorks who fall for such an obvious con. Hell, maybe you are one of those dorks who has been robbed of thousands of pounds in the deluded belief that you will get rich.

Well, here’s what you do if you are Mike Berry. You sit down, make yourself comfortable (because this will take some time) and compose a lengthy response which indicates to the scammer that you are ripe for a fleecing. Then, over the next few weeks, sometimes months, you carefully bait, torment and waste the time of the scammer in dozens more e-mails, letting him believe that you are just about to pay him the £5,000 legal fee that he claims is needed to complete the “ transfer” (there is always a mystery lawyer to pay).

Often Berry dupes them into travelling hundreds of miles to collect the money in person at an airport. Not that he ever shows up, obviously. Or he may trick them into posing for a humiliating photograph (he has persuaded conmen to pose in tutus, in bathtubs with goats or holding up signs stating “I am a thief” or “I s**g sheep” (these are coded messages suggested by Berry to confirm that the scammer is who he says he is). Finally, when he has the scammer on the ropes, he contacts them to say that, surprise! The biter has been bit. “Did you really think I was going to let you steal £20,000 from me?” he usually asks. That’s when he starts getting death threats. But then, that is an occupational hazard for a full-time scam-baiter.

Worldwide it is estimated that more than £1 billion a year is stolen by scammers. Ever day thousands are taken in by them. The fraud might arrive in the form of a letter telling you that you have won millions of euros on the Spanish lottery and must pay an administration fee — usually £1,500 — before the money can be released. But most are what are called 419 internet scams, after the section of the Nigerian criminal code that they violate, and are shameless in their opportunism. Just 24 hours after the Australian conservationist Steve Irwin died, scammers were sending e-mails purporting to be from his widow, asking for help in transferring £3 million of his money out of the country to avoid tax. They even included links to the BBC News website containing reports of Irwin’s death.

Berry sees such e-mails as a challenge. He has created a website — 419eater.com — devoted to exposing and ridiculing the scammers, which now receives 10,000 hits each day. He spends six hours a day, unpaid, attending to the site, when he is not doing his regular job as a computer technician.

What does he get out of it, then? “It started as a laugh,” he says, “but as I got to talk to victims and learn about the tactics the scammers use, it became a bit more serious. I really enjoy doing it. I think of it as a bit of fun but a public service at the same time.”

Berry, 44, lives in a small terraced house in Manchester (we cannot be more specific lest an angry scammer should trace him) with his wife Trisha, his cat and his beloved computer, which occupies a small alcove in the living room. A few years ago he noticed that the number of scam e-mails he was receiving had increased. So instead of deleting them as usual he decided to reply to one and tell him, using a variety of expletives, what a lowlife he was.

Amazingly, he received a reply. The scammer had obviously not read Berry’s missive but assumed that he was a potential scalp and sent a scan of his passport and a clearly faked deposit certificate. Berry typed the man’s name into Google and found that he was a known scammer who appeared on several warning sites. Since then he has devoted half his life to scam-baiting, and has now written a book detailing his counter-stings.

He rummages behind his chair and pulls out a huge wooden carving of his head, a “trophy” from a successful operation. Berry had convinced the scammer that he was an art exhibitor willing to pay good money for quality carvings. There is also a painting that someone has done of his cat. Oh, and someone whom he persuaded to write out an entire Harry Potter book by hand.

One could start to feel sorry for the scammers and, indeed, some people are uncomfortable with what Berry does. The scammers do this only because they are poor with no prospects, they say. Isn’t it faintly racist to ridicule them?

“People say ‘they’ve got no money, no food’, but they don’t realise there are highly organised gangs out there,” says Berry. “I don’t want to paint Nigeria in a bad way. Not all scammers come from Nigeria — they are dotted all over the world. There is a big scamming community operating out of London. But it’s a sad fact of life that the vast majority of 419 scams do originate from southern and western Africa.

“I don’t let them use poverty as an excuse — ‘because I’m poor I’m allowed to steal from you’. The problem, particularly in Lagos, is that the 419 scam is almost a way of life. People are quite open about doing it.”