Derived from the fact that scrumpy is the staple beverage of all gypsies.
Kev : "I dunno dude, ive only got 74 pence!"
Dave: "Thats OK we can buy a whole Gallon of Gypsy Juice for that!"
last weekend we got yiddled on gypsy juice
i made 3 litres of gypsy juice for a buck fifty