AN AMERICAN builder is seeking to usurp an Oxfordshire aristocrat as the head of an ancient Irish family.

And the battle over who is the true Duke of Leinster looks destined to only be settled by the Lord Chancellor.

The dispute has arisen because of the death in 2004 of the eighth duke, Gerald FitzGerald, an aviation tycoon.

His eldest son, Maurice, a landscape gardener who lives in Frilford Heath, believes he is the true heir.

But a builder living in San Francisco, Paul FitzGerald, says he is the rightful duke.

The issue has now gone before the Lord Chancellor in the Department of Constitutional Affairs in London.

Maurice FitzGerald holds the courtesy title of the Marquess of Kildare and is listed in Who's Who as the ninth duke.

But Paul FitzGerald claims he should have inherited the title from his grandfather, Desmond, the second of three sons of the fifth duke, who was believed to have been killed in the First World War.

He says that his grandfather secretly emigrated to the United States and stayed there until his death in 1967.

The American says he has heirlooms and documents proving that he is the rightful heir to the title.

A spokesman for the Department of Constitutional Affairs said: "Both claims are presently under consideration by the Lord Chancellor and Secretary of State for Constitutional Affairs."

Maurice FitzGerald lives in Oakley Park, a private estate near the Bothy Vineyard and Dog House pub.

None of the family was available for comment.

According to records, the late eighth duke had proved his succession to the Viscountcy of Great Britain and took his seat in October 1976 on the death of his father, Edward, the seventh duke, who died in March that year.

The late eighth duke subsequently established formally his succession to the dukedom in March 1977. Following the eighth duke's death in December 2004, his only son, Maurice FitzGerald, submitted a claim through the Crown Office to prove his succession.

The Dukedom of Leinster is the premier dukedom of Ireland, and was created in 1766. Although the Leinsters once had a massive fortune, Edward, the seventh duke, was a chronic gambler and down the years the estate dwindled in size.