The Book of Kells was likely to have been created 1,200 years ago in Pictish eastern Scotland, rather than on the island of Iona, according to research that challenges long-held assumptions about one of the world’s most famous medieval manuscripts.

The Book of Kells is an intricate, illuminated account of the four Gospels of Matthew, Mark, Luke and John that was long thought to have been started in the late eighth century at the monastery on Iona before being taken in the 9th century to the monastery of Kells in County Meath, Ireland, after a Viking raid.

It has been at Trinity College Dublin since the 17th century.

Dr Victoria Whitworth, who will publish evidence in a forthcoming book, said: “The Picts were great artists, producing highly sophisticated Christian sculpture, but it has generally been accepted that not a single Pictish manuscript survives. If the Book of Kells was made in Pictland, this rewrites our understanding of early medieval Scotland.”

Her research has led her to conclude that a monastery in Portmahomack, Easter Ross, north-east of Inverness, is “the most likely place for it to have been made”.

Its monks were manufacturing vellum – the calfskins on which manuscripts were written – as well as creating elaborate carvings with complex inscriptions that match those of Kells, unlike manuscript and carved inscriptions from Iona, which reflect “plainness and legibility”, she said.

Whitworth argued that while the Kells monastery was founded in AD807, it did not become important until the later ninth century. “This is too late for the Book of Kells to have been made at Kells. The Iona hypothesis, while worth testing, has no more intrinsic value than any other,” she said.

Portmahomack flourished as one of the earliest Christian sites in the land of the Picts from about 700 to 800, when it was destroyed by fire, possibly in a Viking raid.

Whitworth said archaeologists had discovered a fine sculptor’s chisel at the site of the monks’ vellum workshop, suggesting that book-making and stone-carving were intimately interlinked.

She pointed to a stone carving – part of a larger cross-slab now in the National Museums Scotland – whose Latin inscription has parallels with the text of the Book of Kells: “It is the most elaborate piece of carved stone from anywhere in the early Middle Ages in the British Isles. It [has] a long Latin inscription in relief, very beautiful lettering that’s very similar to Kells … these fabulous display capitals.

“The art of the Book of Kells is very different from the Iona stone sculpture, which, while high quality, lacks this endless inventiveness and unpredictability.”

It was not until the 1990s that Portmahomack was discovered to have been the site of a major Pictish monastery, through archaeological excavations led by Prof Martin Carver and published in 2016.

Whitworth said previous scholars had argued that the script of the book looked far more like that of manuscripts associated with the Northumbrian island monastery of Lindisfarne than anything associated with Ireland. “The Northumbrian monks are known to have mentored the Picts. However, until recently there had been no Pictish monastery to link it to, and these suggestions were ignored or dismissed. The Picts had suffered for many decades from being seen as mysterious, remote and backward.

“If you just look at the archaeology of our top early medieval monasteries, Portmahomack stands out as exceptionally literate and book-orientated. The standard books will say there are no Pictish manuscripts. We need to flip that on its head and say that the Book of Kells is actually an exceptionally Pictish-looking manuscript.”

Rachel Moss, a professor of history of art and architecture at Trinity College Dublin, said: “During the period when the Book of Kells was made, there is lots of evidence of the movement of holy men, artists, objects and materials across Ireland, Britain and the continent. Unless actually recorded in a manuscript, it is nearly impossible to pinpoint where it was made, or by whom.

“As the Book of Kells first enters the historical record at the County Meath monastery of Kells, historians have traced it back to the monastery from which Kells was founded at Iona. One of the special aspects of the manuscript is how a range of artistic influences from across the known world were blended to form a unique art style.

“Dr Whitworth’s exploration of the manuscript in the context of the archaeological excavations at Portmahomack adds another dimension to the debate.”

Whitworth, who specialises in the art, literature and archaeology of Britain and Ireland AD700-1100, will publish her research in her forthcoming book, The Book of Kells: Unlocking the Enigma, to be published by Head of Zeus in October.

• The Book of Kells by Victoria Whitworth (Bloomsbury Publishing, £35). To support the Guardian, order your copy at guardianbookshop.com. Delivery charges may apply.