More than 1,000 people have been sent back to the Republic by the British authorities over a two-year period.
Figures from the British Border and Immigration Agency (BIA) show that the largest group came originally from Africa, while almost a quarter came from Asian countries including India, Pakistan and China.
The statistics relating to 2004 and 2005 were supplied following a Freedom of Information request from The Irish Times to the British Home Office. This sought details of all people returned to Ireland from the UK.
However, the Department of Justice here said it cannot correlate the figures with individual cases in the State's system, due to the "general and aggregated" nature of the data.
It said additional security challenges arose from the common travel area and land border between Ireland and the UK, but it would be "totally incorrect" to interpret the figures as indicating the presence of a particular security risk here.
According to the figures, 1,065 people were returned to Ireland from Britain in 2004 and 2005.
Of these, 420 came from Africa, including 220 from Nigeria. A further 280 came from Asia, including 75 from India, 70 from China, and 55 from Pakistan.
The figures show that 185 came from Europe, while 45 came from the Middle East, and 40 came from the Americas.
Owing to "data quality" issues, the BIA said it was not possible to provide a more detailed breakdown of cases.
But it said the figures covered "administrative returns", voluntary departures following the initiation of enforcement action against an individual, and "assisted returns".
The figures include people returned following illegal entry. It said people liable to "administrative removal" include those who overstay their visas, those who use deception in seeking and/or obtaining leave to remain, and people whose indefinite leave to remain has been revoked because they are no longer viewed as refugees.
A spokeswoman for the Department of Justice confirmed that 108 asylum seekers were returned under the "Dublin II regulation" whereby individuals are sent back to the State where they initially sought asylum during the period in question. Such cases continue to be treated under the Irish asylum system.
She said only Irish citizens could have been deported to the State during the period.
Figures show that 50 Irish nationals were returned during 2004 and 2005.
"Other categories of foreign national who are removed or remove themselves to Ireland are dealt with under Irish immigration laws . . . it is not possible to comment in a meaningful manner or to attempt to correlate them with individual cases in our system," she said. She said that when a person enters a country illegally and is stopped by authorities, the normal practice is to send them back by the same route.
Such individuals may have had an Irish visa but not a UK visa, and were refused entry.
"It is regularly the case that the foreign national does not purposely intend to breach UK immigration law," she said.