After living together for four years one of my cats aggressively turned on another three months ago, and then started attacking her every time they crossed paths.

The situation briefly got better before getting so bad that Jazz (the victim cat) ran away for three days while I was on holiday.

Upon my return I started researching all possible solutions and frantically tried them all as the bullying got more and more intense.

Eventually Weasel (the aggressor) needed to be locked away from Jazz in the lounge, and my time at home has since revolved around the cats and making sure they both get an equal amount of time outside without crossing paths or being in the same room.

Concerned for all three cats well being (including the super laid back fence sitter, Batman) I looked into getting a cat behavior expert and got referred to Vicky Halls through the Feline Advisory Beureau.

Vicky has since come to visit the cats and has written a report along with instructions on how to get the cats tolerating each other again.
Reassuringly, my understanding of why the cats are behaving in such a way was quite accurate. But her guidance in how to bring them back together should prove to be invaluable.

She has an excellent reputation and her newsletters are well worth reading if you're a cat lover.

*UPDATE*

Four months on and the cats are all back to normal and getting on as they were before.