Michael Franzese knows a fix when he sees one. During a 17-year career as one of New York's most notorious mobsters, he ran a network of illegal bookmakers that preyed on athletes with gambling problems with the express intent of recruiting them to insider betting.

It was an extraordinarily simple and successful operation. He outlined a typical fix: “The bookie calls me and says, 'Hey, Mike, this guy's into us for $10,000 [about £6,000].' I say, 'Let him be into you for $100,000,' because the deeper he gets, the better it is for us. I might even have him receive a losing tip. Soon he's in debt for $200,000. He comes to me and I say I'll charge 1 per cent interest a week until he pays it off. So then he's betting more, trying to get even, and before he knows it, he's into me for his life.

“So I tell him, 'Here's the deal, your team is favourite to win by ten points - you're gonna win by five. We don't want you to lose, just don't cover the spread. You pull it off, we're even; you screw it up, you're gonna be in a hospital.' That's it. Very simple.”

So simple, in fact, that Franzese says anyone who does not believe this kind of corruption is still rife in professional sport is “kidding themselves”. “It's happening a lot,” he said. “Organised crime is always involved in gambling.”

Now aged 58, and a reformed character after serving eight years of a ten-year prison sentence for gasoline bootlegging, Franzese makes his living writing books, giving lectures and advising sports officials how to prevent their players falling into the traps he used to set.

His work with the ATP attracted attention this side of the Atlantic when it came to light just weeks before the sport was engulfed in a suspected betting scandal in 2007. Betfair, the online betting exchange, had voided the £3.4million market on a match in Poland between Martín Vassallo Argüello, a low-ranked Argentinian, and Nikolay Davydenko, the Russian ranked No 4 in the world at the time who eventually withdrew with an injury, because of suspicious activity.

A subsequent review by the tennis authorities, led by two former policemen, Jeff Rees and Benn Gunn, concluded that the professional game was “neither systematically nor institutionally corrupt”. Davydenko was cleared of any wrongdoing.

Before last year's Wimbledon Championships, Ian Ritchie, chief executive of the All England Club, insisted that tennis “did not have a problem”, despite the admission that eight matches would be investigated because of unusual betting patterns.

With Wimbledon starting a week today, work has been under way for five months at a new integrity unit based in London and led by Rees. In the aftermath of the Davydenko scandal, more than a dozen players came forward to say they had received approaches to throw a match. Franzese corroborates their stories.

“I have had contact with lower-seeded players who've said to me that an hour before the match, on which they make maybe seven or eight grand, somebody came up to them and said, 'I'll give you $20,000 if you blow this match,' ” he said. “These players know they're never going high in the ranks so this is a big payday.”

He understands the Russian players to be the “most vulnerable”. “I was involved with Russian guys in the gasoline business,” he said. “They targeted players with families back home who were afraid if they did not do their bidding, their families would be hurt.”

There is more than a touch of the dramatic about Franzese, but he does have first-hand experience of the people intent on exploiting sport, particularly basketball and American football. “Guys on the street don't care what sport they corrupt so long as they make money,” he said. “Athletes are sophisticated in their sport but on the streets, they're babes in the wood.”

He believes illegal gambling on sport is more prevalent than in the 1980s because of greater access through online betting. “I had 12 bookmakers working for me but now you go online and you're away,” he said.

Despite his insider knowledge, he admits the best he can do is educate athletes. “I'm just informing the players so they can't say they're ignorant,” he said. “Am I putting a dent in the business? I doubt it.”

Echoing Martina Navratilova's call for a lifetime ban on players caught match-fixing, Franzese says the punishment needs to be harsher. “The penalties should be severe,” he said. "You gotta scare these people.”

Sending round some of his former associates ought to ram home the message.

Goodfella to good guy

Michael Franzese became a made member of one of New York's five Mafia families aged 24.

His father, Sonny, who was the underboss of the Colombo clan, wanted his son to become a doctor, but the heir apparent dropped out of medical school to take the oath to the Cosa Nostra.

He rose swiftly through the ranks to become captain in 1980 and built a reputation as a sharp black-market operator. He made more than $300million (now about £180million) during an illicit career that was the most successful since Al Capone, according to federal investigators. His most lucrative business was gasoline bootlegging, but his activities extended to union kickbacks, gambling, loan sharks and white-collar fraud.

He soon became the subject of repeated racketeering charges - Rudy Giuliani, New York's federal prosecutor who later became mayor, promised to jail him for 100 years but the case failed.

Then Franzese met Camille Garcia, a dancer and devout Christian who convinced him to change. He struck a plea bargain for ten years on a racketeering charge and, upon his release, rejected the Mafia life. “Nobody has left the Mob without joining a government programme, especially at my level,” he said. “I was a hunted guy for years. I didn't testify against anyone but they took years to calm down. I outlasted just about everybody in my life - they're either dead or in prison.”

His second book, Blood Covenant, is being made into a film. He says the most realistic Hollywood films about the Mafia are Donnie Brasco and Goodfellas.