2001 Census
The 2001 UK census was the first which allowed British citizens to express an Irish ethnicity. In all previous British censuses, figures for the Irish community were based on Irish birthplace. The percentage claiming White Irish ethnicity in England and Wales was 1.2 per cent, with the highest concentration found in the London Borough of Brent, where they made up 6.9 per cent of the population, while the figure for Scotland was 0.98 per cent. The Irish have been the largest source of immigrants to Britain for over 200 years and as many as six million people in the UK are estimated to have at least one Irish grandparent. As many as one in four Britons may claim some degree of Irish ancestry although there is no reliable hard data on the question.
Read more about this topic: Irish Migration To Great Britain