Re the opium poppies, I read somewhere (and I cannot remember where, nor can I find a reference to it, having looked), that Nevill had a licence for growing these, for the purpose of selling them to the pharmaceutical industry. Can't say whether this is true or hearsay, I'm afraid.
The opium poppies are a mystery. According to police surgeon Dr Craig shortly after JB was told about the deaths he was found wandering around the yard clutching a bunch of poppies. JB told Dr Craig the farm had a licence to grow opium poppies for the pharma industry and yet the first UK licence granted by the gov to grow opium poppies in the UK was late 90's/early noughties. And the licence was with the pharma company not the farmer.
Dr Craig asked Chief Sup Harris if the farm had a licence to grow opium poppies and he didn't know anything about it. The pair had a look at the field where they were growing.
Of course if you were growing opium poppies on your land for the black market this is a very good reason for not calling the police.
By all accounts NB was a pillar of the community so growing opium poppies for the black market would seem out of character and yet they haven't been explained.