Re: £300 million?
My local CCG made everyone go electronic, the argument being someone would have to approve the request and avoid over ordering of medicine. I doubt this happens much, if at all.
As said elsewhere, the secure nature of the prescription pad adds to the cost.
Certain members of society are keen to get their hands on blank pads so they can create their own prescriptions (or sell the pads to others so others can).
In some areas / clinics the printer trays for prescriptions have locks on to deter thieves.