Which type of tree with poisonous berries is often found in uk churchyards and has a starring role in the film "a monster calls"?

It would be the yew tree.

Yew (Taxus baccata) is a typical tree of churchyards, where some are thought to be well beyond 1,000 years old. Poisonous yew trees were planted in churchyards by the farmers to make sure that their animals didn’t stray into them. "They stop and sleep under the yew tree (the monster), but in the morning, the young woman is dead, having been murdered, and the shocked young prince is covered in blood."