Going back to the original question of why Jeremy didn't call 999 - I can quite categorically say, that had my dad called me to tell me my brother had a gun (he was also schizophrenic), I'd have called 999. He also had never been violent but I would have been equally concerned that he may have hurt himself as well as wondering about the safety of my parents. However, there was no urgency - why?
Because something similar had happened before and had calmed down on its own?
Freddie Emami had called Nevill, because he could not control Sheila during an "episode". Dotors couldn´t control her during this episode, and Freddie was scared to death.
However, Nevill didn´t see this as an emergency, so he took his time coming to London. Why didn´t he?