English: You are either an Englishman born & bred in the Home Isles, or the descendants of English colonists in one of the Union's many far-flung outposts and domains. Along with the other Home Nations, you are the foundation of the Imperial Union - without you, there can be no Britannia. The English are sociopolitically the most versatile of the Empire's people, and thus you can come from pretty much any social background and take on any political position you want.
Anglo-Irish: You are of mixed English and Irish heritage. Perhaps your ancestors came with the Normans in the initial English invasion of Ireland back in 1169, or perhaps they were more recent arrivals. In either case, you are likely to form part of the ruling aristocracy on the eastern half of the island, or at least to be wealthier and more privileged than most Irish, and you will definitely be living by English common law rather than the native Gaelic laws followed by the Irish outside the Anglo-Irish nobility's feudal domains. Other Anglo-Irish will be quicker to trust you in most cases, but the native Irish resent your privileged background and the very nature of the blood that courses in your veins, and will more frequently question your motives even if you're trying to help them - after all, that's what your ancestors were probably saying to theirs in the past, too.
Irish: You are either an Irishman born & bred on the Emerald Isle, or the descendants of Irish colonists in one of the Union's many far-flung outposts and domains. Your ancestors were some of King (and later Emperor) Charles's most stalwart supporters, having benefited greatly from his rule, and you are almost certainly no different; it doesn't help that you still enjoy great privileges as outlined by Charles. The Irish are also known as the Imperial Union's most fervent Catholics, and though generally not as violent as the Puritans who loathe them (and who they despise in return), like your countrymen you have no problems with standing up and loudly defending your faith. The Irish still enjoy considerable autonomy on the Emerald Isle, or at least the ruling class does - the peasantry and artisans tend to suffer as they always have, and worse yet if they happen to be a serf bound to the local Anglo-Irish lord.
Scots-Irish: You are of mixed Scottish and Irish heritage. Your ancestors may be the Scottish Presbyterian settlers called in to colonize the Ulster Plantation, only to be violently driven out or underground (or, you know, killed) by the angry native Irish after the final defeat of the Scottish National Covenant in 1653. Alternatively, like the powerful MacDonalds of Carrick, your ancestors may have instead aligned with the Emperor and the Catholic faith in those dark days and were rewarded for it. In any case, you belong to and yet are still distinct from both worlds; the Irish may fear that your kind will try to colonize them or otherwise resent you for the same reasons they resent the Anglo-Irish, while the Scots fear that you will interfere in their politics to strengthen your own definitely non-Scottish powerbase.
Highland Scots: You are either a Highlander born & bred in Northern Scotland, or the descendants of the many Highlander soldiers stationed as colonial garrisons in the Empire's early days. Like the Irish, your ancestors benefited tremendously from Emperor Charles's rule, and the Highlands still retain a great degree of autonomy today; of course, that may actually be a bad thing, as these privileges and sweeping autonomy has allowed the Highland clans to keep fighting each other for trivial reasons. Highlanders have been guaranteed freedom of religion since 1645, and to this day can still proudly display a non-Catholic faith in public without fear of repercussions from the British Inquisition.
Lowland Scots: You are a Lowlander born & bred in Southern Scotland. The Lowlanders are generally much less supportive of the Crown than the rest of the Home Isles, and for good reason - due to their constant resistance against King/Emperor Charles I, your people have been locked out of administrative positions, faced heavy discrimination toward their Low Church Protestant (specifically,
the Presbyterian Church of Scotland) and generally treated as the black sheep of the Home Isles. The British Inquisition is always present to clamp down on any non-Catholic religious displays, and indeed works much harder in the Lowlands than anywhere else in the Isles - there's still a sizable minority of (underground, but still) 'heretics' for them to brutalize here, after all.
Welsh: You are of Welsh ancestry, born & bred in Cymru. Your people were and still are the butt of many jokes involving sheep, but you've never forgotten the fact that you are the closest of all the British peoples to the earliest Britons - something you and your people have held with pride, even after nearly 700 years of English subjugation - and many Welshmen dream of the day that they take their place in the sun as a valued and properly respected member of the Imperial Union (which would also hopefully put an end to those irritating sheep-shagger jokes).
Foreigner: You come from another land. Perhaps you are a dispossessed aristocrat, out to secure yourself a nice new estate and maybe even some serfs? Or a mercenary, a vulture seeking to grow fat on the blood of the constantly-feuding Irishmen? Whatever the case, you're in Britannia now and leaving will be rather expensive, so you'd better come to like it here...you may come only from France, the Netherlands, Iberia, Italy, Sweden, Denmark-Norway or the Holy Roman Empire.