Don, "It was caused as much by British Inheritance laws as they applied to Ireland as anything else." I'd heard that the inheritance laws of splitting the land between all the sons was an Irish thing - I'd never heard of it being a law imposed on the Irish by the British. This link seems to say the same. Any info? Incidentally (to add another musical aside), Show of Hands' song "Man of War" is about a (Dorset) man serving in the Navy because the newly-split farm isn't large enough to support his family.
Using Google, which knows all... :-) Guest TBR, this link says 8.2m to 6.6m. Also note that many Irish emigrated to Britain for work in the new factories (as indeed did many English people, who were also suffering from the potato blight, and from a coinciding cholera epidemic). This link puts the Irish population of Liverpool as 22%.
Oh, and (first link again) "Between 1815 and 1914 about 16.4 million emigrated from Britain. About 11 million went to the USA, 2.55 million to Canada, 2 million to Australia and New Zealand, and 850,000 to South Africa. Of these 16.4 million about 4 million were from Ireland." Coffin ships were not exclusively the preserve of the Irish.
PS. Please don't make me out to be a typical Brit making excuses. The thought of what the landowners did makes my blood boil. But the English landowners were doing it to their tenants on the other side of the Irish Sea as well, and not all landlords were English in any case which kind of twists the knife worse. It ain't just as simple as the "Brits screwing the Irish again".