OH dear. En route to Simon Singh’s mews home, tucked behind Portobello Road market, my pit-of-stomach dread of maths — fractions, long division, impenetrable formulae — resurfaces. This is an old, primal fear and not Singh’s fault. He has done his utmost to soothe the nerves of maths-haters (arithmo-phobes?) like myself.

His new Radio 4 show, Another Five Numbers, is a lively series of 15-minute journeys around numbers and their “social and scientific history and significance” — four, for example, is the only number with the same number of letters as the number itself, but also, apparently, the least colours you need to draw a map without two neighbouring countries sharing the same hue.

Singh, a bear of a man dressed in retro Hawaiian shirt and boffin-issue circular specs, is a zealous advocate for maths and science. His first book, Fermat’s Last Theorem (1997) was an international bestseller, shifting 200,000 paperback copies in Britain alone. It told the amazing story of how a Princeton academic, Andrew Wiles, finally proved the 17th-century mathematician Pierre de Fermat’s 300-year-old theorem — that while the square of a number can be broken down into two other numbers squared, the same is not true of cubes, or any higher power.

Besides the number crunching, this was also brilliant drama, starting with Fermat’s tantalising jotting next to his theory: “I have a truly marvellous demonstration of this proposition which this margin is too narrow to contain.” With considerable verve, Singh charted how generations of ambitious thinkers had resorted to theft, transvestism, even duelling, in their efforts to prove Fermat’s theorem.

Wiles became obsessed by Fermat at the age of nine. At the same age, Singh declared his intention to become a nuclear physicist. His family had been farmers in the Punjab, though his grandparents had moved to Somerset in the 1930s. (He is researching their history to find out why.) His parents took on the family business, a clothes shop, which mutated into the New Look fashion empire.

“My parents left India with virtually nothing,” he says. “They couldn’t speak English, they had no idea how they would survive in England and they were leaving behind everything they owned and everybody they knew. The journey that they made, and the success that they achieved in a new country, will surpass anything that I will ever achieve. When I saw the sacrifices they made, then there was a real responsibility to do well.”

Despite initial pressure from his parents to enter the business, he was “cut some slack” to study. His teachers at secondary school — Mr Stephens (maths), Mr Mynett (physics) — “loved to see students get excited about the things they got excited about and they knew enough about their subject to stretch those kids that were bright.”

His father, meanwhile, showed him “how things worked”. He jumps up from the sofa and returns with something his father made, a “dozel”, a little stick with grooves on it with a mini-windmill on its tip. He uses a second stick to rub against it, and on my say-so (the magic word is “hooey”), the windmill goes into reverse. This isn’t magic, apparently — it’s simply a question of where you position your fingers. As a boy, Singh was transfixed by TV scientists such as Magnus Pyke and Heinz Wolff exclaiming vividly over “videos of what the Universe was like, why the sky is blue, why you shut your eyes when you sneeze”.

After A levels in mathematics, physics and chemistry, Singh studied physics at Imperial College, London, then for a PhD in particle physics at Cambridge and at the European Centre for Particle Physics in Geneva. It was there, aged 26, that he decided to leave academia.

“It would have been great to have made some fantastic discovery. There can’t be anything more wonderful for a scientist than to be the first person to know the answer to a problem. But I realised the people around me were pioneers and I wasn’t.” His voice falters. “I just wasn’t smart enough and I was around people who were.” Later, he says: “It was a time when I’d given up hope. You suddenly realised that you’re not going to be getting your Nobel Prize, that you’re not going to be making the greatest discovery, that you’re not going to be published in Nature.

“From the age of ten, I had wanted to be a scientist. Perhaps this compounded my depression when I realised I wasn’t smart enough to be a great scientist.”

But having taught for a year in an Indian school, he knew he was good at conveying complicated ideas. “I had this skill that’s fairly useless in science, where you are promoted or ditched on the quality of your research. I could communicate.”

IN 1990 he joined the BBC and for six years made films for Horizon and Tomorrow’s World. He was approached to direct a film about Fermat while considering a career change; it was a huge success, winning a Bafta, and Singh wrote a book telling the whole story. He watched with mounting incredulity its rise “from eight to five to three then one” in the book charts.