This is not a quote, per se, rather, it is a meme. It is attributed to Gilbert Gray, and according to The Independent Saturday 7 March 1998 was originally:
"I take it, Mr Gray, that your client is familiar with the maxim: Quis
custodiet ipsos custodes?" "Indeed my lord, responded the QC drily.
"In Barnsley they speak of little else."
However, according to the Fortune Newsletter two years later, it was attributed to a different barrister, Charles Gray, who is reported to have recounted
a story about a barrister in Reading who was asked by the judge
whether his client was aware of the principle of Res ipsa loquitur
(the thing speaks for itself), to which the barrister replied: "In the
Irish village from which my client comes, M'Lud, they speak of little
It is also attributed in 2005 to some unnamed judge referring to sic utere tuo ut alienum non laedas.
As Tim Lymington notes, the Irish res ipsa loquitur version is attributed to Marshal Hall apparently was on the air in the BBC production The Trials of Marshall Hall originally from 1996, and is cited in a recent book review. The book review and Wiki versions of that statement differ slightly in the wording of the text, to wit Wiki:
"Is your client not familiar with the maxim res ipsa loquitur?”
replied, "My lord, on the remote hillside in County Donegal where my
client hails from they talk of little else."
vs. book review
Judge: “Mr Marshall Hall, is your client familiar with the doctrine
res ipsa loquitur? Marshall: “My Lord, in the remote hills of County
Donegal from where my client hails they speak of little else.”
Without a copy of the book, I can't say whether the reviewer mis-copied the quote, but at least we can believe that the linked quote represents the review author's wording. There is a much earlier work on the life of Marshall Hall, Marjoribanks, Edward For the Defence. The Life of Sir Edward Marshall Hall K.C. (The MacMillan Company, New York, 1929), which might contain the quote in question. At this point, I am inclined to take the Hall res ipsa loquitur quote as being original and the others as being derivative works.