Steve and Sam Williams, 39, whose parents emigrated from Nigeria in the early Seventies, spent four years working on the software behind their Populous PPT currency in the family home in Brockley.

It helps small and medium-sized businesses with cash flow. Within the first five days of launching in June last year, demand was so strong that the initial batch of tokens was worth more than £8 million.

Populous is now rated as the 51st most valuable cryptocurrency in the world out of about 2,000, with a market value of about £100 million.

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They own 16 million Populous “tokens” worth a total of $55.3 million (£42.3 million) at today’s price of 3.46 cents per token. At the peak of the Bitcoin frenzy at the start of the year their holding was valued at close to £1 billion.

The success means that Sam now lives in a Knightsbridge apartment and Steve, who lives in Essex with his wife and two young children, sends his six-year-old to private school. Their offices are in Mayfair and they have become friends with stars, such as rapper 50 Cent and boxer Floyd Mayweather.

Steve Williams (right) and brother Sam with rapper 50 Cent

In the brothers’ first newspaper interview, they told the Evening Standard that the outcome could have been very different as they were “always in trouble” as schoolboys.

Steve, who is older by one minute, said: “It was very tough in terms of gang violence. You had no choice: you either got bullied or you pretended to be part of one of the gangs to safeguard yourself.”

The three-bedroom terrace where they grew up with their mother, a chef, accountant father and sister, was so cramped that Sam sometimes had to sleep on the sofa.

Steve studied advanced business in sixth form in Lewisham, while Sam took a course in computer programming.

In 2008 Steve was charged and convicted of obtaining money transfers by deception and served 18 months of a three-and-a-half-year jail term.

He said the experience “made me learn a lot about what it means to be a victim of crime and how it impacts on them. It filled in some elements that were missing in me and opened my eyes to what could happen to me.”

Sam has since launched two other crypto coins called Zloadr and DocTailor, aimed at legal professionals. Steve added: “We have gone through a lot together as brothers and it is great that all our hard work has paid off.”