Rolaaand. Mate, thanks but I don't need clarification. I surely understand the difference, but obviously many pilots in the ME region don't? I'm just trying to find something in the ICAO documents on this topic...something of that kind in FAA, UK CAA or Eurocontrol's documents is useful as the reference but not mandatory in this region ...
Capt. Claret. Clearances such as " when ready..." are appropriate and acceptable ONLY in hours with low density traffic...when the !!!! hits the fan- trust me, I'm not arguing with the pilots - descend means
now 
I'm just curious, if you know the difference between descend and descend when ready, why are you asking " now or when ready"? Instruction was clear and understandable? While I was working in Europe, I never encountered misunderstanding of that kind, it started when I moved to the sandpit...
Cheerz