Experimenting on one of my apps on my phone, I noticed that the cashback app Receipt Hog will accept Diamond single and day (Diamond only products) tickets as a valid receipt for cashback.
It may only be 0.5p for receipt under a tenner, but for regular users, it does add up (and eventually can give you a couple of singles in cashback - or a fiver off a shopping bill!)
Has anyone else used a cashback app with their diamond bus tickets?