Other mistake: There is a scene where Miss Potter is in the Lake District beside a lake drawing. Across on the other side of a lake there is a red car driving along the road quite fast. This is in the cinema version.
In the scene at the Christmas party Mr Warne tops up the coffee cup with brandy to give to Miss Wiggins. At this point the cup is full to the brim but when he then carries a tray with this cup on it looks barely full.