It's called politics. Manufacturer Abbott announced (Nov 1st I think) that it has secured reimbursement listing for the flash glucose monitoring system on the NHS Drug Tariff after getting the green light from the NHS Business Services Authority. By coincidence it also got FDA approval and Abbott's share price jumped while Dexcom (another CGM) dropped.
It is a nonsense as there isn't even a way of getting it at the £35 they charge pharmacies. My local Boots would want £47.50 after their markup, the pharmacist checked for me the other day, at least he was honest with me.