People born in Northern Ireland, part of the UK, have a similar tradition of migration to Britain as their counterparts in the Republic of Ireland. But an added factor for the past decades has been the Troubles.
Unlike the Republic, the number of people in Britain born in Northern Ireland went up between 1991 and 2001.
Most of the increases have been in Scotland – there are long-standing ties to both the Protestant and Catholic communities – while London is one of the regions where numbers of Northern Ireland-born has gone down.
The 2011 census will show whether a "peace dividend" in Northern Ireland will affect migration.