Lord James Douglas-Hamilton, the Scottish health minister who sits in the House of Commons, claimed the title and the pounds 500,000 of family heirlooms that go with it, when his uncle, George Douglas-Hamilton, the 10th Earl of Selkirk, died in 1994.
But days later he renounced the House of Lords honour because, he said, he did not want to resign from the Commons and force a by-election threatening John Major's majority. He retains the courtesy title "Lord" as the son of a duke.
After his sacrifice, the title lay vacant. Lord James, 53, assured relatives that it would stay in the immediate family when he died, passing to his 17-year-old son, John Andrew. But the old Etonian's plans were upset when his cousin Alasdair Douglas-Hamilton challenged his right to be ennobled.
Alasdair, 56, argues that he, and not Lord James, is the rightful heir to the earldom. Late last year he lodged his claim at the Court of the Lord Lyon in Edinburgh, set up in 1672 to settle genealogical disputes north of the border.
Although the two cousins have avoided all but the most gentlemanly exchanges on the subject, the internal conflict in Scotland's most important aristocratic family has captivated polite society, anxious to see battle joined in court.
The pinstripes of Scotland's "hooray Hamishes" were on bold display yesterday as the Lord Lyon, Sir Malcolm Rognvald Innes of Edingight, began to hear the evidence. Through his counsel, Alasdair Douglas-Hamilton argued that a 300-year-old family document proved that he should inherit the title.
The document, known as a diploma, is contentious. Not only is it written in Latin, making it inaccessible to all except classical scholars, but there is doubt over its true meaning. It was drawn up by the first Earl of Selkirk, William Douglas, after his family was joined with Scotland's other great aristocrats, the Hamiltons, when he married Anne, Duchess of Hamilton, in 1656.
Marriage meant that William became Duke of Hamilton as well as Earl of Selkirk. He thought it was wrong that one man should hold both titles and through the diploma he ensured that in future the earldom would always go to the younger brothers of the Duke of Hamilton.
And so it did until 1994 when George Douglas-Hamilton died. His title could not revert to his brother, former Tory MP Lord Malcolm, because he was dead - the victim of a plane crash. As the younger brother of the current Duke of Hamilton, Angus, Lord James Douglas-Hamilton, concluded the earldom was his.
In court yesterday, however, counsel for Alasdair argued that the diploma made it clear that the succession should pass along the line of brothers - and, if necessary, sons of brothers - until the line was exhausted. As the son of the late Lord Malcolm, he, and not Lord James, was entitled to the honour.
But counsel for Lord James said it was wrong to skip a generation; the title should rest with the man known in the Scottish Office as "the gent". After the hearing the two men insisted they were "still friends".
"What is important is that this business is sorted out absolutely and amicably," Lord James said.
Judgment is expected in April. Whoever loses is likely to appeal to the Court of Session, Scotland's highest civil court, and, if necessary, to the House of Lords.
For Lord James, the case could end in the place he sought to avoid when he renounced the title two years ago.Reuse content