“ Worse for the drinkers was that taxation also encouraged the adulteration of tea, particularly of smuggled tea which was not quality controlled through customs and excise. Leaves from other plants, or leaves which had already been brewed and then dried, were added to tea leaves. Sometimes the resulting colour was not convincing enough, so anything from sheep’s dung to poisonous copper carbonate was added to make it look more like tea. ”
UK Tea Council : Tea 4 You : Tea - A Brief History of the Nation’s Favourite Beverage
Oh the interesting facts you find when writing radio programs… Sheep dung tea!