Ok an update, after getting the wiring diagrams from Subaru ( thank you Subaru customer support ) the offending current draw was narrowed down to the rear boot. ( SBF No 8 feeds all the internal fuses near the steering column ).
On disconnecting both the lift mech and closure mech, much the same as far as current draw, but the vehicle wouldn’t alarm despite the boot being correctly shut.
All the wiring checked out so being left with only components I fitted a new rear sill latch and voila, the boot now shuts like a Swiss watch compared to the old mech and the stand by current is down to 0.07A’s.
A note here, the alarm system is sensitive to anything moving, even ever so slightly on the side. If you are testing standby current, you will need to have the bonnet closed, stand still at the front, alarm the car and wait 30 seconds before the standby current will begin to drop. If you move at all the alarm will wake and begin to draw current.
Another note, you can’t fit a manual sill latch, the bolt pattern in the tailgate is different.
Subaru U.K. advised that all vehicles post 2013 have been fitted with the updated rear boot controller and yet the rear sill latch for some reason wasn’t allowing the vehicle to fully shut down. A bit of firmware not working in harmony somewhere.