Just read your Spectator article and, like you, I did not know the snowdrop was not native to Britain.  However most websites seem to think it was introduced in 16th Century eg https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/plants/wild-flowers/snowdrop/

Thought you would not want your next 100 Years War story to get this wrong!

Thanks for all the great books,

Rob