Fauja Singh is something of a celebrity at the east London gurdwara (Sikh temple) which he visits daily. While he tucks into a breakfast of rice pudding and a cup of tea on a sunny Thursday morning, a steady stream of people approach to congratulate him on his latest achievement. He smiles and chats, his eyes twinkling. Just days before, he completed both the Luxemburg Interfaith marathon and the Edinburgh marathon as part of the relay team Sikhs in the City - a team of four Sikh elders with a combined age of 336.

Fauja is the oldest of the four, a sprightly 98 but, as I interview him, with the help of his trainer-cum-mentor-cum-manager-cum-friend and, for today, translator, Harmander Singh, he exudes a boyish charm that makes you forget he's close to 100.

Fauja first ran when he was a youngster in India, but returned to the sport after a 54-year gap to complete his first marathon at the age of 89. He says he took up running after losing a son and later his wife - these losses left him demoralised and saddened and he felt he needed a new focus in his life. He moved to Britain and soon started challenging other old-age pensioners to races. He chuckles cheekily as he explains how he increased his competitive edge: "If they looked healthy, I'd extend the distance; the races got longer and longer until I ran my first official race - a 20km run for Cancer Research UK in 1999."

Once bitten by the running bug, he set his sights on the London marathon and with the help of Harmander he gained a place running for Bliss - the premature baby charity - making him the oldest person in the race running for some of the youngest.

"I didn't really feel tired after crossing the line, which was partly down to the training but mainly to God. He put me there so he had to help me finish! I thought: 'I'm going to do more of these.'"

Since then, Fauja has run six more marathons - another four in London, one in Toronto and one in New York - and he has broken 12 UK, European, Commonwealth and World records, though he remains remarkably humble about his accomplishments.

"I only weigh 52kg," he says. "It's not a lot."

All four members of Sikhs in the City share an infectiously positive outlook and lust for life that is key to their ongoing success. Ajit Singh, 79, for instance, has just learned to ride a bicycle, so one of his goals now is to complete a triathlon. He and his lifelong friend Amrik Singh, also 79, have completed more than 1,000 races between them and acted as mentors to Fauja. Karnail Singh, 80, is the newest member of the team and the least experienced runner. His "experimentation" with course routes means that his teammates have to keep an eye on him, but what he lacks in kilometres he more than makes up for in providing the focus for a little gentle mickey-taking.

The Sikhs in the City are familiar faces on the marathon scene and are treated to a warm reception wherever they go, but Fauja in particular has become a bit of a global star. Having completed marathons in America, Europe and Asia, he was recruited as the face of Adidas for their "Impossible Is Nothing" campaign in 2004. He has also been the subject of an online petition to be recognised in the Queen's Birthday Honours and there is even a "Fauja Singh Appreciation Society" on Facebook.

How does it feel to be on the receiving end of so much public adoration? "It makes me happy," he says. "Elderly people are like little children, they like attention."

The running quartet are in agreement about why they've managed to stay so healthy: a positive frame of mind, keeping the company of people who are forward looking, not indulging in any excesses, appreciating what God has provided them with and keeping active.

And for Fauja age isn't even a consideration:

"I do not consider myself to be old. From the moment I do that, I would lose everything, because age is a state of mind - as long as you're positive you can do anything."

None of the four have any intention of hanging up their trainers. In the next four months alone they're taking part in a relay marathon in Redbridge (east London), a relay from Birmingham to London, attempting to notch up yet more records at the Norway KnarvikMila where times are age-weighted, and they are joining a British team with a total age of 1,000 years at the Toronto Waterfront marathon to challenge a team of Canadian elders over a 5km course.

For Fauja the answer is simple: "I won't stop running until I die. The next target, God willing, is to be the oldest marathon runner ever." The title is currently held by a Greek man who completed a marathon aged 98, but as nobody seems to know his exact date of birth, Fauja is holding fire until he turns 99 and the following year, when he will be 100, he would like to return to the London marathon - his home course.

Before leaving I ask Fauja what changes he has seen in Britain in the 15 years he's been here and he replies in his typically charming, upbeat way. "Maybe it's because I'm getting on a bit and so I'm grateful for everything, but despite what other people might say, I only see improvement. The respect and acknowledgement I get here is just wonderful." And with that trademark twinkly smile he adds: "I am very grateful for the opportunities I have been given. If I didn't do any of this why would a man like me, of my age, have the opportunity to wander the streets of the world?"
Laura Potter