It seems a waste of a GP's precious time to have to prescribe what should be a coeliac patient's routine/ repeat medical treatment.
However, should a local CCG recommend the cutting of all GF prescription items in their area they cannot chop off the head of a GP who prescribes those items to an individual coeliac patient who has been diagnosed with CD by NHS.
The CCG might try to threaten to refuse reimbursement of the cost of GF items thus prescribed but the patient's GP is the person who has the duty of care for each individual patient and I don't think any such GF prescriptions have been questioned by a CCG.
It is the GP who decides, in his or her professional opinion, whether or not a certain patient needs certain prescriptions, this is a GP's legal duty.
As with any prescriptions, if the GP thinks a coeliac needs GF scrips s/he can prescribe them (as long as the items are not on the NHS blacklist and I believe ACBS GF basics are NOT on that list).