There is a small, windowless room on the ground floor of Oxford’s Radcliffe Infirmary that can be reached only by walking through a maze of narrow passageways. The hospital, built in the late 18th century, is old even by the normal standards of ageing National Health Service buildings. Nevertheless, it is in these antiquated surroundings that scientists have set up one of the most ambitious biological programmes attempted in Britain.

This is the base of the People of the British Isles project, which is using the power of modern genetics to show how people in different regions interacted over the past few thousand years, how they subjugated one another and how they passed on ideas, inventions and art.

In that little cubbyhole on the ground floor there is a bench fitted with high-technology gear used to isolate and copy DNA, a couple of tables with personal computers and several tall fridges. Inside these are rows of vials that hold the bloodline of the British people. Each vial contains DNA from a person who has taken part in the project and each sample has its own special story to tell.

Blood was collected from 11 sites for the project’s pilot study: Orkney, northeast England, Cumbria, Lincolnshire, Norfolk, Suffolk, Oxfordshire, Pembrokeshire, Kent/Sussex, Devon and Cornwall. The researchers then used centrifuges to isolate the white cells, which are stuffed with DNA. Using the DNA — and thanks to advances in molecular biology — the team has begun to build up a pattern of different genetic variants for different parts of the British Isles.

From the moment they started to pull data from their machines, their findings produced fascinating information about one of the most conspicuous aspects of the British and Irish population: our redheads. Whether they are called carrot-tops, ginger-heads or “Titian blondes”, these people are blessed — or cursed, according to some of them — with flaming locks that have been a feature of people for millenniums, from Boudicca to Prince Harry.

The underlying causes of the condition were recently disentangled by a team led by Professor Jonathan Rees, a dermatologist based at Edinburgh University. It was discovered that hair colour is controlled by a gene called the melanocortin 1 receptor, or MC1R. Genes come in different variants and there are about 70 different versions of MC1R. Rees discovered that a subgroup of about half a dozen is closely involved in determining if a person will be red-haired or not.

“If you have one of these variants, your chances of having red hair are increased four or five times above the average,” said Rees. “However, if you have two of these variants — one inherited from your mother and one inherited from your father — your chances of being red-haired increase to 30 to 40 times the average.”

(This is exploited by forensic scientists when testing blood left behind at crime scenes. If they find two MC1R variants, police know there is a strong chance the culprit will be a redhead.)

Red hair today is generally associated with the Scots and Irish, but there have been no consistent efforts to establish the prevalence of the condition.

“It has actually become harder to find the prevalence of red hair today,” said Rees. “More and more women — and some men — now dye their hair and we simply have no idea if a redhead is a real one or if a blonde is a redhead under the dye. As a result the incidence of red hair in Britain is still a bit of a mystery.”

Enter the scientists of the People of the British Isles project: thanks to their efforts, this most distinctive characteristic is now opening up its mysteries for the first time. Testing their white cell samples for two of the half-dozen red-hair versions of the MC1R gene, they were able to show their frequency in each area of the British Isles. The results were intriguing.

Where one is the maximum value, they got figures of 0.16 and 0.23 for the frequencies of red-hair genes in Cornwall and Devon. The frequency in Oxfordshire was 0.07; in Sussex and Kent 0.13; in northeast England 0.11; in Lincolnshire 0.07; and in Cumbria nil. In Wales the figure was 0.21, and in Orkney a high 0.26. But the highest was in Ireland. Using data from other research studies, the team got a figure for Ireland of 0.31, confirmation of the stereotypical image of the red-haired Irishman.

The results are remarkable, as Sir Walter Bodmer, the Oxford geneticist leading the project, acknowledges: “I was amazed at them. I didn’t expect to see something like this.”