He made a similar claim in Folk Song in England (1967), some years later, but again provided no references or evidence:

"...we know that the wren-hunting song was attached to a pagan midwinter ritual of the kind that Church and authority fulminated vainly against - particularly in the rebellious period at the end of the Middle Ages when adherence to forms of the Old Religion was taken to be evidence of subversion, and its partisans were violently persecuted in consequence".

In this respect, Lloyd was a bit of an unreconstructed Frazerian; and we should bear in mind that the hypotheses of writers like Margaret Murray were not discredited until after he wrote that. We should also bear in mind that he is not actually saying, in the later book, that the ritual dates from that period; just that it is like some (unnamed and unidentified) that, in his opinion, did.

If anyone has any concrete evidence of the practice of hunting the wren as early as the 14th century, please let us know about it; ditto for the song, though in the absence of references earlier than (so far) the first half of the 18th century, I'm guessing that to be much later.