I meant to mention it in my review of the book (which appears elsewhere in this newspaper today), and somehow forgot. But an unfortunate feature of The Collected Letters of Flann O’Brien was his tendency in later years to use a certain N-word that, unforgivable now, was even then pushing the boundaries of polite usage.

The habit arose from his last novel, The Dalkey Archive, in which, thanks to some time-bending experiments by a mad scientist called De Selby, the 4th-century Bishop of Hippo, Saint Augustine, makes a cameo appearance in the Dublin suburb of the title.

To judge from his correspondence, the real-life Flann, Brian O’Nolan, did a lot of historical research for the novel: perhaps more than was in the best interests of comedy.

One of his resulting obsessions was the discovery that Christianity had invented the Holy Ghost only in AD 381, or at any rate the concept had not been mentioned anywhere before that.

But an even greater preoccupation was with St Augustine’s skin colour, about which he suspected there had been a Jesuit-organised cover-up.

Hence his fondness, when writing to friends and publishers from 1962 onwards, for repeatedly raising the issue in rude terms, and one term in particular. He even took to putting the question in capital letters, as when he mentioned (to someone from the BBC) that he had been in contact with the British Museum seeking certain information about Augustine, viz: “We all know that he was a heretic and a voluptuary but my sole perplexity is WAS HE A NIGGER?”

This continued, periodically, for the next two years, as he became more and more of an expert on the saint but still couldn’t establish from textbooks what he looked like.

For the committed Flannorak, the frequency of the N-word’s use in his letters of the time is embarrassing. It’s a bit like having an old family pet who breaks wind constantly when you’re entertaining visitors. Or, maybe more aptly, like having a small boy in the house who, having learned a bad word that shocks adults, can now not be stopped from saying it in company.

There is, in general, a manic quality to the 1960s letters, when O’Nolan’s advancing alcoholism and ill-health were competing with the excitement of rediscovery as a novelist and the struggle to do new work.

It also caused him to range between utter certainty and severe doubt about the worth of what he was doing, as in a 1963 letter to the writer Leslie Daiken. In that, he tells Daiken the new book is “a fucking masterpiece” [it wasn’t], adding that it had been delayed by a research problem, which remained unresolved, viz: “WAS AUGUSTINE A NIGGER?”.

The editor of his letters anthology, Maebh Long, clearly shared the general reader’s mortification at this and other crudities, commenting in a footnote that O’Nolan’s “views on race [...] unquestionably disappoint”.

But in mitigation, she cites a 1943 column in this newspaper wherein, as Myles na gCopaleen, he had blamed racism for the genocide happening in Europe.

Indeed, in later years, Myles also attacked the IRFU over playing rugby matches against apartheid South Africa, although that may have been as much to do with his general dislike of the sport’s “alickadoos”, and a reluctance to miss any opportunity to put the boot in, than with social justice.

By an interesting coincidence, in a 1962 letter with no mention of anyone’s skin colour, O’Nolan’s compares himself to Mark Twain, whose printed use of “nigger” in 1876 continues to cause headaches for literary editors and teachers, especially in the US, today.

No matter that The Adventures of Huckleberry Finn is the Great American Novel or that, on the questions of slavery and racism, it is on the side of the angels. Such is the negative power of that one word in the 21st century, the novel is still being banned and bowdlerised.

Even by the mid-1960s, the usage was increasingly forbidden. So when the then young playwright Hugh Leonard adapted The Dalkey Archive for stage, he substituted “black” for the description of St Augustine that had finally made it into the book.

O’Nolan protested that “black” was a “neutral, humbug term” and argued, disingenuously, that it was a jeering De Selby who was using it, not him.

Leonard countered that theatre audiences might not appreciate this distinction. Besides, it would be an unnecessary distraction. The N-word was “such a bomb [...] these days”, warned Leonard, it would “throw the play out of gear with a bump”.