Cheers for the replies guys.
We generally do maintain the speed profile even when off the SID as you suggest, to be safe than sorry! But I suppose it's just another case of the theory versus the practice.
However, not all pilots will adhere to speeds and or passing altitude at XXX requirements when recleared or taken off the SID/STAR track. Unfortunately, the book will say they're not wrong. Danceswithsheep, I agree with your note regarding advising ATC of any deviations to ensure everyone is in the loop. Has to be the safest option.
Many thanks,
CP.