According to Hogg, writing at the end of the 19th century, this plum was raised by Jervaise Coe, a market gardener living in Suffolk at the end of the 18th century who developed several plum varieties of which Golden Drop has been the most successful.
Coe stated that he raised it from a Green Gage pollinated by a White Magnum Bonum (a large culinary plum). Whilst Coe's Golden Drop has the sweet rich gage-like flavour, it seems to benefit from being balanced somewhat by the acidic qualities of its other parent which prevent it becoming over-sweet. If there is a recipe for perfect flavour in the plum world, the marriage of the old Green Gage with a true plum is probably the best place to start.
Whilst pure gages are invariably small and round, Coe's Golden Drop has the slightly oval appearance common to many plums. The fruit is also relatively large - certainly by gage standards. It can be kept in a fridge for more than a week, which is very unusual for any plum - although the combination of its excellent fresh flavour and the fact that it is not a particularly good cropper means you probably won't have enough to be worth keeping.
If you can't find Coe's Golden Drop, it is worth looking out for Jefferson - Coe's Golden Drop is thought to be one of the parents, and Jefferson has a similarly good flavour but is a bit easier to grow.