That source was Father Etienne Robo in John White: Two Brothers (1939), in which he erroneously reverses the birth order of John the Elder and Younger, an error which is mistakenly repeated by others, regarding him as their authority.
Father Robo is particularly harsh in that short booklet in his judgement of John the Grocer, as was also observed in a review in the journal Economic History of his book, Mediaeval Farnham: Everyday Life in an Episcopal Manor (1935):
“His attack on John White, the Lord Mayor of London, rests, to all appearances, on a non-sequitur; the fact that a man purchased Church lands for a good round sum is surely not proof that “sordid interest made [him] a supporter of the New Religion”.
The review also notes that in his treatment of the Reformation at Farnham:
“Father Robo disarms criticism by explaining, with the courtesy of the old religion, how hard he has tried to be just; may I suggest as courteously as a heretic may, that he has not altogether succeeded?”.