This is who Jesse Sheidlower is:Instances of f**k before the 15th century are rare. Despite it commonly being classed as one of the Anglo-Saxon four-letter words, Jesse Sheidlower (author of an entire book on f**k, and past editor of the OED so he knows what he's talking about) suspects that it came into English in the 15th century from something like Low German, Frisian or Dutch.
http://www.jessesword.com/
All of which is to say that he may be considered qualified to discuss the word's history, or if you agree with Borrobil, maybe not.