Further investigation produces this. And there's also "Bonus fact: This quirk of yew trees made them highly desirable for making bows in ancient times. The light coloured sap wood has great tension qualities so it's used for the outside face of the bow, allowing it to flex. The heartwood has great compression qualities, used for the inside face, it can store up a lot of energy. The demand for yew was so high that they chopped down most of the trees in Europe at the time. Only ones on consecrated ground, protected by the church, managed to survive the genocide. The supply got so low the king of England brought in rules that said if you were bringing anything to a port by ship, there was a tariff of a certain quantity of yew bow staves (which are the strips of wood which are hewn down to make the bow). Luckily the invention of the rifle was right around the corner. Lucky for the yew tree that is." That chimes with my memory, but again is non-specific about the tariff. My memory says there was, at one time, a link with wool (we used to export a lot to the Low Countries), but I can't find any evidence, so my memory may be playing me false!