Can only offer a guess, as Flanders has traditionally been a pass-through point for contending armies throughout the ages. I have a version of this particular song on an old (1980's?) tape by the group "Scartaglen". Having listened to the words, I would take a stab at guessing it comes from the mid-1700's--possibly the Seven Years' War, but I could well be wrong. There are a lot of songs out there that sound very traditional (meaning from generations past), but are actually quite contemporary. My guess comes from the mention of brandy and sack--I don't know if the British Army has a brandy ration these days (someone feel free to correct me--please), and sack was, I think a sweet food or some sort of drink. That's the best I can do; I hope others will be able to shed more light on the matter for you. Great song, by the way! Cheers and good luck.