As an RAF controller I am not aware of any regulation on this. I stand ready to be corrected (we are good at that on here). The only (RAF) guidance I have ever had on the subject it is to only give one instruction at a time to student pilots and then to give vertical instructions before lateral ones.
As a qualified pilot, I will expect you to be able to take multiple instructions. I would give you the instructions in the order I think most important at the time because, being human, that is the order in which you will usually carry them out. So if the climb is most important, that goes first. If I need you to turn more than climb, the hdg will come first. I will, of course, split up long transmissions so as not to confuse numbers, to allow some poor sod with a snag to get a word in and to prevent our transmissions being DF'd
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