The inspiration for Mr Charming, my account of the life and crimes of a Ponzi-style fraudster, came from an unlikely source: one of his victims. Over the years, a very dear and old acquaintance had often remarked that I really must meet her new best friend: a wonderful German chap by the name of Felix Vossen. He was great company – funny, well-read, emotionally sensitive and highly intelligent. In his spare time, he was a film producer. But his day job was financial trading. He was an investment guru who ran a fund worth £250 million from his offices in London and Zurich. Much of my friend’s money was invested in that fund.

Felix the film producer: with Charlotte Rampling and his fellow producers from Embargo Films at the premiere of I, Anna at the Berlindale Film Festival in 2012. Vossen claimed he could raise a £10 million fund to help Embargo produce a series of movies. (Mr Charming: The Life and Crimes of Felix Vossen, Amberley Publishing)

Imagine then her utter shell-shock and despair – and my own surprise – when he also turned out to be a fake and a compulsive liar. A cheat and a charlatan who had run off, not only with my friend’s money, but also the life savings of scores of other victims. Some £45 million in all.

In the days and weeks that followed Vossen’s abrupt disappearance, I reflected on my own narrow escape: how often I had been due to meet Felix at various dinner parties and birthday celebrations that he had failed at the last minute to turn up to. And whether I too would have been drawn into his web of deceit by his easy charm and absolute plausibility. Inevitably, I also spoke regularly and at length to my friend and her husband about the case. How were they coping? Had they traced any of the money? Had anyone discovered his whereabouts? What were the police doing?

Felix in one of his various guises. (Mr Charming: The Life and Crimes of Felix Vossen, Amberley Publishing)

And then one day, during a long walk in the country, my friend said: ‘Why don’t you write a book about it? It’s right up your street.’

I didn’t need a second invitation. The name alone, FELIX VOSSEN, conjured up an image of a James Bond villain. Although we had never actually met, I could picture him in my mind’s eye, reclining in a Parker Knoll chair stroking a white cat.

During a career in financial journalism, I had written about a great many crooks, fraudsters, chancers and psychopaths – a few of whom had also been the CEOs of FTSE100 companies. The story of Felix Vossen was not only a tale of financial skulduggery. It was also about personal betrayal and regulatory failure and the woefulness of banking supervision, even in these modern, sophisticated and inter-connected times.

In order to tell his story, however, I needed to tell the stories of his victims. And that meant gaining the trust and confidence of a fractious and vulnerable group of individuals for whom trust was at a very low ebb. They had believed in something that had proved too good to be true and been left financially ruined, emotionally bereft, and psychologically-damaged by someone they too had grown to regard as their best friend. Why should they trust an outsider, and a journalist to boot, to recount their experiences in a balanced, sympathetic and non-judgemental way?

What followed was several months of negotiation to re-assure his victims that although they might feel guilty for the plight that had befallen them, there was only one real villain of the piece: Felix Vossen. Some were happy to co-operate, others declined. Some would only take part with a guarantee of anonymity.

Cash, false passports, laptops and mobiles seized by Spanish police from Vossne's apartment in Valencia after his chance arrest in February 2016. (Mr Charming: The Life and Crimes of Felix Vossen, Amberley Publishing)

A short way into the researching of the book, the dynamic changed dramatically. Felix Vossen had been found. He had been arrested by chance in the Spanish city of Valencia after arousing the suspicion of a passing police motorcycle patrol and extradited to Switzerland, where he was wanted on charges of fraud, money laundering and forgery. Not only would he face justice, but his victims might achieve some form of closure, even if it might take a bit longer to recover their stolen money. To this day, only £100,000 or so of the £45 million he stole has ever been recovered.

Their best chance of being made financially whole again is to apply pressure to the banks that Vossen deposited their money with and hope that compensation is forthcoming. To succeed, they will probably need to do more than rely on the corporate altruism of those banks or embarrass them into coughing up. Instead, they will need to demonstrate negligence in the way that Vossen was supervised and his accounts were monitored.

In the spring of 2020, Vossen himself will walk free from prison in Switzerland, where he was eventually tried and convicted. Perhaps he can help.

Michael Harrison's new book Mr Charming: The Life and Crimes of Felix Vossen is available for purchase now.