Good find David 
I've thought for a long time now illegal drugs play a much bigger role in this case than we currently fully understand.
I remain sceptical about the whole idea. There are several things you need to consider.
1. Growing opium for illegal production of Heroin in the UK is more or less unheard of. There is no money to be made. Illegal Opiates are lucrative because farmers in Afganistan, Turkey, Laos and Vietnam grow opium for peanuts. poor nations with perfect weather conditions. I cannot see any UK farmer seeing it worth while.
2. The pharmaceutical industry is much bigger and more lucrative than the illegal drug industry. Legitimate and regulated opium sells for a lot more than what peasant farmers in Afganistan and Laos charge.
3. Just because there was no opium in Neville's blood test does not rule out self medication because the growing season had not finished.
4. The police found out about the opium at WHF and made no big deal about it. This supports the argument that production was legal. That "special license" could have been the authorities using their discretion to deal with a short supply of the drug.
5. If Neville was the heroin kingpin of Essex using Pharmacuticals as a ruse. Its most likely Jeremy was not in on it and took Nevills word for it. Otherwise he would not have called the police to the farm nor would he unwittingly walk Dr Craig into the opium plantation.
