Buster Martin, who is famous for still working as a part-time valet at a plumbing company in central London, raised more than £20,000 for charity after completing the marathon on Sunday.

He was born in France and moved to a British orphanage as a baby. He has a Home Office certificate of naturalisation but has not been able to produce a birth certificate.

A spokeswoman for Guinness World Records said: "We have to be quite stringent. If we do not have sufficient evidence we cannot verify it." She added: "It is a real shame because it is such a lovely story."

The remarks by Guinness World Records come after a report that Mr Martin could be as "young" as 94.

The spokesman for the Guinness World Records said she could not comment on the report but said their decision was made "purely" because they did not have the required documentation .

A spokeswoman for Pimlico Plumbers said Mr Martin completed the marathon in just under 10 hours and had raised more than £20,000 for the Rhys Daniels Trust, which provides accommodation for families close to specialist hospitals while children are under going life-saving treatment.

She said: "Charlie Mullins (the managing director of Pimlico Plumbers) has never had any reason to doubt him. This was never about a mention in Guinness World Records, this was about raising money for the Rhys Daniels Trust.

"Quite frankly, whether he is 94 years old or 100, what he has done is just amazing."

Mr Mullins said: "He is adamant that is his age. That is what he told us and we did all the standard checks and they all came back to us that that his how old he is."

Guinness World Records lists the oldest man to complete a marathon as the Greek runner Dimitrion Yordanidis, aged 98, in Athens in 1976. He finished in seven hours, 33 minutes.