The lead is promising, though much of the letter is paywalled.

"Sir, I am — as he knows — an enthusiastic admirer of Giles Coren, but he is badly misinformed about Wikipedia (“Why stop at Trump?”, Dec 12). As a writer of history I resort to it at least a dozen times a day. I could never have written my last two books without it, and I have never caught it out yet, which is more than I can say of the Encyclopedia Britannica. Its range is astonishing: it is almost impossible to find a person, place or subject that it has left uncovered (end of my preview).... a work of reference as useful as any in existence..."