If you get paid to fly people/animals/boxes, for a third party you need an AOC, it don't matter what you chuck in the back, the CAA wants its cut.
On a seperate note, you will need approval from DEFRA also.
Routes and transport companies « Defra
The real question is what if you fly birds, and they fly unhindered in the pax compartment, are you really carrying them? I guess as soon as they defecate you are again carrying something so you need a "sh!tty" AOC.....
At least we have a thread again where the vicious pro private and pro AOC can have a go at each other again on how much safer they each are......
Hat, coat, door.