For civil aircraft in Class G airspace, the speed restriction is 250Kts maximum BELOW FL100. An exception is if the aircraft cannot comply for airworthiness reasons, however a CAA exemption is required for this.
None of the above exempts an aircraft complying with a published speed for a published procedure such as a hold or a STAR.
Looking at the Edinburgh plates, there is a 250Kts speed limit either 3 minutes flying time from the holding facility or when crossing the Speed Limit Point. But this doesn't apply until you are FL140 or below. So you could crack on in at high speed for another 6000' feet of descent in your example (minus any time needed to slow down to 250Kts before passing FL140 if you are within the 3 minutes flying time or past the SLP), unless instructed by the controller to fly a specific speed for separation/sequencing.