Today, millions of residents of Great Britain are either from Ireland or have Irish ancestry. It is estimated that as many as six million people living in the UK have at least one Irish grandparent (around 10% of the UK population).
The Irish diaspora (Irish: Diaspóra na nGael) refers to Irish people and their descendants who live outside Ireland. This article refers to those who reside in Great Britain, the largest island and principal territory of the United Kingdom.
During the Dark Ages, significant Irish settlement of western Britain took place. The 'traditional' view is that Gaelic language and culture was brought to Scotland, probably in the 4th century, by settlers from Ireland, who founded the Gaelic kingdom of Dál Riata on Scotland's west coast. This is based mostly on medieval writings from the 9th and 10th centuries. However, recently some archeologists have argued against this view, saying that there is no archeological or placename evidence for a migration or a takeover by a small group of elites. Due to the growth of Dál Riata, in both size and influence, Scotland became almost wholly Gaelic-speaking until Northumbrian English began to replace Gaelic in the Lowlands. Scottish Gaelic remained the dominant languages of the Highlands into the 19th century, but has since declined.
Before and during the Gregorian mission of 596 AD, Irish Christians such as Columba (521–97), Buriana, Diuma, Ceollach, Saint Machar, Saint Cathan, Saint Blane, Jaruman, Wyllow, Kessog, St Govan, Donnán of Eigg, Foillan and Saint Fursey began the conversion of the British, Picts and early English peoples. Modwenna and others were significant in the following century.
Some English monarchs, such as Oswiu of Northumbria (c. 612 – 15 February 670), Aldfrith (died 704 or 705) and Harold Godwinson (died 1066) were either raised in or sought refuge in Ireland, as did Welsh rulers such as Gruffudd ap Cynan. Alfred the Great may have spent some of his childhood in Ireland.