I haven't heard the adjective "jollopy" before, but jollop was a term used in northern England in the days before the national health service refering to a bottle of patent medicine bought over the counter. Could be for coughs e.g. liquafruta, could be a laxative (there seemed to be a great belief in the benefits of a good clear-out)
Possibly jollopy tea was stewed so much that it tasted unpleasant like medicine.
Or could it be the belief that the army put bromide in the tea to stop the soldiers sexual drive?