The larger majority of Irish people living in the U.K. are less likely to identify themselves as British, according to 2011 census data.
Fewer than 40 percent of Irish people living in the UK identify themselves as British, compared to more than 80 percent of many other ethnic groups.
More than 91 percent of Irish people born outside of the UK do not hold a UK passport, compared to 45 percent of Indians born outside of the UK and 31 percent of Pakistanis born outside of the UK.
Chris Smith, of the Office of National Statistics, said Irish immigrants tend to maintain a sense of national identity throughout their time in Britain.
He said: "Irish migration goes back to the 1840s, it was 9 percent, 10 percent of the population of some parts of England in the 1880s, 1890s: very, very high proportion.
"But they seem to maintain their sense of national identity despite the length of time here."
The census breakdown shows that 1.54 million moved to the UK in the decade to 2011, compared to 880,000 between 1961 and 2000.
At least 7.5million immigrants now live in Britain, making up 13 per cent of the total population, according to the data.