The difference here is that I know a lot less about the way English is spoken in Ireland than I do about how it is in India and with Indian expatriates. (So take everything following with a perhaps larger than usual grain of salt.) It seems to me that McCrum's claim that there is a distinctively Irish dialect of English (that is, something quite different than a mere accent) seems quite weak in this chapter. I tend to speculate that the closeness of Irish English to 'standard' English is a necessary consequence of the nearly complete disappearance of the Irish language (Irish Gaelic) as a naturally spoken tongue in Ireland. Many people in Ireland know some Irish because it is widely taught in the schools, but almost no one is a monoglot Irish speaker. There is less to bounce off of, and not much reason (geographically or politically) for the kind of linguistic isolation that produces real dialects -- like Jamaican patois.
One doesn't learn much about "Irish English" as a linguistic phenomenon from reading this chapter of A Story of English, but it is a nice survey of the linguistic theme in the writing of some important Irish writers. McCrum quotes the poet Seamus Heaney describing the Irish language as "mythically alive," which is kind of sad, in one way of thinking about it. On the other hand, the "myth" of Irish is an animating feature in the work of many Irish writers (even if, as in Joyce, it only appears as a thing to be scoffed at).
McCrum et al. mention my favorite literary example -- the Mrs. Malaprop character in R.B. Sheridan's play The Rivals (available online in pieces at Bibliomania). Mrs. Malaprop is the bumbling character whose name eventually gave us the standard English word "malapropism," and McCrum reads her as a kind of index for the learner's mistakes many Irishmen in the 18th century might have made as they attempted to master English (and, steadily, to forget their mother tongue).
It seems plausible, though it's important to keep in mind that Mrs. Malaprop's mistakes are all bookish mistakes rather than 'learner' mistakes. They aren't examples of Irishism so much as undisciplined Latinism -- a 'vocabulary' run amok:
Lydia. What crime, madam, have I committed, to be treated thus?
Mrs. Malaprop. Now don’t attempt to extirpate yourself from the matter; you know I have proof controvertible of it.—But tell me, will you promise to do as you’re bid? Will you take a husband of your friends’ choosing?
Lyd. Madam, I must tell you plainly, that had I no preferment for any one else, the choice you have made would be my aversion.
Mrs. Mal. What business have you, miss, with preference and aversion? They don’t become a young woman; and you ought to know, that as both always wear off, ’tis safest in matrimony to begin with a little aversion. I am sure I hated your poor dear uncle before marriage as if he’d been a blackamoor—and yet, miss, you are sensible what a wife I made!—and when it pleased Heaven to release me from him, ’tis unknown what tears I shed!— But suppose we were going to give you another choice, will you promise us to give up this Beverley?
Lyd. Could I belie my thoughts so far as to give that promise, my actions would certainly as far belie my words.
Mrs. Mal. Take yourself to your room.—You are fit company for nothing but your own ill-humours.
Lyd. Willingly, ma’am—I cannot change for the worse.
[Exit.
Mrs. Mal. There’s a little intricate hussy for you!
There's a little intricate linguistic jugalbandi (warning: amusing link) for you.
The other classic example is J.M. Synge's Playboy of the Western World (available online at Project Gutenberg), which really does have a number of Irishisms in it:
PEGEEN -- [impatiently.] He is surely, and leaving me lonesome on the scruff of the hill. (She gets up and puts envelope on dresser, then winds clock.) Isn't it long the nights are now, Shawn Keogh, to be leaving a poor girl with her own self counting the hours to the dawn of day?
SHAWN -- [with awkward humour.] -- If it is, when we're wedded in a short while you'll have no call to complain, for I've little will to be walking off to wakes or weddings in the darkness of the night.
PEGEEN -- [with rather scornful good humour.] -- You're making mighty certain, Shaneen, that I'll wed you now.
SHAWN. Aren't we after making a good bargain, the way we're only waiting these days on Father Reilly's dispensation from the bishops, or the Court of Rome.
PEGEEN -- [looking at him teasingly, washing up at dresser.] -- It's a wonder, Shaneen, the Holy Father'd be taking notice of the likes of you; for if I was him I wouldn't bother with this place where you'll meet none but Red Linahan, has a squint in his eye, and Patcheen is lame in his heel, or the mad Mulrannies were driven from California and they lost in their wits. We're a queer lot these times to go troubling the Holy Father on his sacred seat.
Synge (pronounced like "Singh") is pretty clear in his preface to the play that he's trying to capture the voices of late nineteenth century Irish peasants in the western part of the island, where the Gaelic language and Gaelic patterns of speech lingered on through the 19th century. As a result, it's impossible to imagine the voices of this play performed in anything other than a thick Irish brogue. But then, I've never seen this play performed anywhere. (Has anyone seen it done?)
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I'm also teaching Joyce again, in parallel with this. (Perhaps a post on Joyce's Portrait of the Artist as a Young Man might be forthcoming.)