Britain had always been the principal destination of Irish migrants, whether they went only for seasonal or permanent work.
It should be remembered that unlike the Irish emigration to USA, Australia and Canada, there are no records of passengers leaving Ireland on ships to England, Scotland and Wales as they were not recorded on embarkation nor disembarkation. This is because Ireland was considered a part of Britain until 1922.
The lack of passenger records can create problems. However, the UK census records can be of some help in discovering Irish ancestors. But it should be noted the census records only record Ireland as birth place, very rarely do they give a county.
For the purpose of locating Irish born Casses. I looked at the census records from 1841 to 1911. I’ve also included not only those born in Ireland but also their English born families