So what you're saying is his joining clearance would have been passed to Brize and should have been relayed to the pilot by them.
It was thus either an omission by Brize ATC or maybe it was given to the aircraft but Ice pack wasn't aware for some reason eg lack of CRM. I know this is possible as crew members may listen to different frequencies quite often, but then the clearance should have been either received by or relayed to the captain, who should have briefed the other crew members with something like 'ATC joining clearance received and acknowledged'