Hi, and welcome Dean,
Have you tried using pheromone diffusers such as Feliway or Pet Remedy? There are also Beaphar Calming Spot On, and Zylkene which is added to food, not sure how it works, it's essentially a milk protein, but it does. It stopped inappropriate behaviour between my five.
You can get Pet Remedy as a spray too, put it on your hands and then rub over the cat. It does help.
I hope that's of assistance.