RESEARCHERS believe they have uncovered a "genetic frontier" which separates Britain's Celtic nations from England.

Geneticists analysing thousands of male DNA samples from Scotland, England, Wales, and Ireland were baffled after discovering a number of of Y chromosome clusters among the Celtic populations - indicating that large numbers of modern men are descended from a handful of ancient kings or patriarchs - but finding no such patterns in England.

In Wales, the research indicates that almost one in five men - 19 per cent - are descended from only ten kings or patriarchs who reigned between 1,000 and 1,500 years ago.

In Scotland, around half of men with the Stuart or Stewart surname - regardless of the spelling - are believed to be descendants of Sir John Stewart of Bonkyll, a 13th Century nobleman who fought alongside William Wallace and whose subsequent lineage includes the Stuart monarch, James VI of Scotland.

Other "royal bloodlines" are also being traced, including potentially a genetic marker identifying descendants of Robert the Bruce.

Although England has always had a much large population than Scotland and Wales, researchers on the ScotlandsDNA project, which conducts parallel DNA studies across the British Isles, believe they would have found genetic clusters by now, if they existed.

They believe the contrast may be down to historic differences in how inheritance was passed down centuries ago, with England traditionally following a 'primogeniture' model, where the eldest son inherits everything, whereas Celtic culture practised 'partibility', where inheritance was evenly shared.

Alistair Moffat, historian and co-founder of ScotlandsDNA, said: "You would expect that William the Conqueror's noblemen, who became very wealthy as a consequence of the conquest, to have access to lots of women and to father a lot of children, and they almost certainly did.

"But because those children, if they were illegitimate, unlike in Celtic society, weren't recognised, or even if they had sons by the same woman, only the eldest son inherits, their sons and grandsons and so on gradually become less and less powerful, which in turn means their ability to access lots of women really diminishes.

"So you can see within quite a small number of generations how that power could dissipate completely.

"But it doesn't do that in Celtic society. In Scotland and Wales, it sustains itself. That's because, firstly, illegitimate children are recognised and, secondly, the principle of 'partibility' means everyone gets something."

The Norman invasion in 1066 laid the foundations for primogeniture because the new king of England relied on 20 large and wealthy landowners to supply him with soldiers. If landholdings were broken up, his ability to recruit and army would have weakened.

In comparison, in Scotland, clans formed armies through kinship ties. In Ireland, Turlough O'Donnell, a 14th Century lord, epitomised the mantra that "powerful men can breed an army" by accruing more than a thousand great-great-grandsons thanks to his prolific breeding.

"It's two different views of power," said Mr Moffat. "One is based on land, primogeniture; and the Celtic one is based on family. But they both have the same purpose: to create military dominance."

Mr Moffat said the hunt for genetic clusters, effectively long-lost royal bloodlines, in England was a "lost cause".

He said: "You would expect to find a glimmer or a hint by now, but they're just not there. The upshot is that the Scots and the Welsh are much more royal than the English.

"It's as though you cross the Cheviots and it changes. It's a real genetic frontier."