Claudr, you could be right about NICE. My speculation comes from this -
scroll down and you find -
"That this House welcomes the recent announcement that named patient prescribing for Sativex has been approved for multiple sclerosis sufferers; notes with concern that this will cost an average of £4 per day for patients; calls on the Government to work with the Medicines and Healthcare Products Regulatory Agency to license the drug to enable NHS prescriptions; and calls on primary care trusts to make funds available for individuals in the interim."
If GW have agreed some discount with the Home Office, or the NHS, that would count as a "deal".