I read it wrong - but wonder how the Dr would know about a licence?
Dr Craig was a police surgeon with 30 years experience so I assume he was very familiar with the widely used pain relieving drug morphine, which as I'm sure you know is derived from the opium poppy. I assume he was also aware of how it was produced and all the processes surrounding it ie licensed poppy farmers overseas. By this I mean he would probably be aware it was grown overseas under licence so asked if WHF had a licence. That's one explanation. Another explanation, as per CAL's book although it's unsourced, is that JB told Dr Craig WHF had a licence:
Page 179:
"He [JB] was carrying a small bunch of opium poppies when Dr Craig caught up with him. Explaining that the farm had a special licence to grow them for the pharmaceutical industry..."
Blue has one WS only from Dr Craig and there's no mention of opium poppies but he might have made other WS's which CAL had access to via the CT but as I said CAL hasn't quoted her source.
Was it possible (and legal) that WHF had a licence to grow the poppies for an overseas pharmaceutical company? As the Bambers were tenant farmers did they have complete autonomy over operations or did the trustees of the Henry Smith Charity have a say? If the former was there anything that prevented NB negotiating, either directly or indirectly, with a foreign government/pharmaceutical company to farm opium poppies? If the latter maybe NB was following instructions from the trustees.
As NB was a RAF pilot in WW2 I am sure he would be more familiar than most with many aspects of morphine.