Oh, I’ve had a lovely time reading up about trees in general and spindle in particular.
It would seem that the berries of the spindle tree are indeed toxic, causing abdominal pain, vomiting and diarrhoea in humans and also affecting dogs, cats, horses and goats. Not sure if cattle or sheep would be affected, but didn’t find any specific mentions. Possibly sheep are too canny to eat it - ex-BH had fields with yew overhanging and we never had any problems with the sheep. (Cattle didn’t graze that field, it was a sheep only field - not because of the yew but because of the tourism!).
I also found, which is obvious now but I hadn’t realised, that the wood of the spindle tree is very hard and used to be used for... think about it... spindles!
(Not quite the right emotiwotsit, but it was the closest we have.). Now I definitely want to grow some