@BrianTheElder So sorry you had to go through that - I'm not allowed my antidepressants on repeat prescription, so if I can't get an appointment I go through exactly that.
I think you are exactly right about the arrogance of GPs - I also take two medications for a heart condition. The hospital clinic has written to the GP asking them to take over prescribing, and so I toddled off to the GP, expecting no problems. In fact, they refused to prescribe one at all, and only gave me, rather randomly, 25 days of the other.
I also think perhaps it is a system flaw - given all they can do with the computers, surely it wouldn't be too hard to flag up, if you request a prescription within 30 days of the review date, that you need to book a review appointment?