Ken Matthews of Swansea is in discussion with Home Office forensic scientists about the best way to exhume members of the Talbot Fletcher family for DNA fingerprinting tests, which he believes would show he is also a Talbot Fletcher. He is receiving backing from his local MP, Donald Anderson.
He is not motivated purely by a desire to claim an inheritance. Mr Matthews is suffering from a mystery illness which causes fainting that doctors have been unable to diagnose. They believe it may be hereditary.
At present, members of the family lie at rest in their private chapel at Margam Castle, their former home near Swansea. Margam was sold in the late 1930s but the family continues to own estates in East Lothian and north London.
In 1900, Lady Emily Charlotte Talbot was one of the richest women in Britain, with a legacy valued in those days at pounds 6m. The family gave Port Talbot its name and derived part of its fortune from Fox Talbot, the photographic pioneer.
Mr Matthews was adopted and only traced his connection with the Fletcher Talbots when he began to investigate his natural roots. He found that his real mother was Ivy Pinn, who worked at Margam Castle as a maid in the 1930s.
She left in 1937 when she became pregnant with him. He was eventually given up to the workhouse in Neath and was later adopted. His birth certificate says his father is unknown and records of his adoption are missing from the Neath court where they should be lodged.
Diligent detective work enabled Mr Matthews, who works in the personnel department of a car factory, to locate two half-sisters he never knew he had. They told him about his mother, who died in the Midlands, aged 78, in 1988.
Gradually, the pieces came together. In videotaped interviews, former Margam workers told Mr Matthews his mother had a 12-year affair with John "Jock" Theodore Talbot Fletcher, the master of Margam and 11th Laird of Saltoun, in Scotland, and he was the result. "I had no suspicion at all," said Mr Matthews. "When I was told Jock was my father I couldn't believe it - I was looking for a groundsman or stablehand."
John Talbot Fletcher inherited Margam, its 12,000 acres and other estates, when he reached 30 in 1933. He was left them by his great aunt, Lady Emily, who specified in her will that when he died, the legacy should go to his eldest son. But Mr Talbot Fletcher had no legitimate children. Perhaps significantly, his marriage was annulled within days of Mr Matthews's birth in 1937.
Before Mr Talbot Fletcher died last April, aged 91, he was visited by Mr Matthews in Epping, Essex, near the family's Cropped Hall estate. He was pleasant recalled Mr Matthews, until Ivy's name was mentioned. Then the conversation was abruptly ended.
Mr Matthews then wrote to Mr Talbot Fletcher requesting he take a DNA test. He received a terse response from Mr Talbot Fletcher's Cambridge solicitors, Mills and Reeve, saying: "It is totally wrong and inappropriate to trouble a man of his age with such matters."
Mr Anderson, said: "As a lawyer I'm always pretty sceptical about these stories but there is very strong circumstantial evidence. The recordings with the old retainers confirm it was common knowledge the master of the house was having an affair with the maid." But Francis Durrant, of Mills and Reeve, said: "There isn't a claim as far as we are concerned."