When an amendment is made to a clearance, the new clearance must be given in full to the pilot by the air traffic controller, and this new clearance automatically cancels any previous clearance.
This phrase is what I was getting at. You choose to put that only into the context of if the level is changed any other level restrictions are cancelled unless restated in the new clearance. The phrase above clearly states that when issued with a new clearance the clearance cancels any previous clearance. That said as I outlined in my examples, does that mean that any restrictions that were issued as part of that original clearance are cancelled along with the clearance.
Example. ABC cleared DESDI for the DESDI 4V arrival descend FL150, speed on the descent not above 270 kts Indicated.
Next call is ABC you are now recleared direct to UKRUM for the ILS RWY 12L, descend A100 QNH 1012.
As far as your quote from the UK CAA Ops Notice to pilots, says subsequent clearance cancels previous clearance. Does that also cancel the speed restriction that was part of the original clearance?
BTW I still think in the case given where,
An aircraft is given a clearance, 'descend FL150, cross XYZ FL180 or below' and then receives another clearance of 'descend FL130'. Does the 'cross XYZ FL180 or below' restriction still apply?
that the restriction is automatically cancelled, is crazy and in my opinion open to errors by pilots and controllers alike.
Also I don't appreciate the condascending tone about the amount of traffic in someones airspace. We all have our unique challenges and the airspace around Dubai has more than its fair share. Try working with the Iranians for a few days and see how you get on.
For Neptune, maybe the alternative (since the existence of this need for clarification means that despite what PPRune Radar says this isn't black and white for everybody) is to make the whole situation crystal clear for everyone by making it that any requirement but me specifically cancelled by a controller otherwise it continues to be required. Seems pretty crystal clear to me.