Uni with things liek Diazepam you really should be getting better advice than the average GP.
I was put on a course because I was told I'd have to wait up to 6 months for an operation, I was in quite tremendous pain (I'd frequently pass out if I was doing something as strenuous as going for a wee) and the chronic insomnia (15 hours a week sleep) was taking its toll. The problem was I just needed a painkiller, idealy one other than codine.
I find addiction very easy for a mind like mine.
Luckily I was taken off it very quickly by a different doctor.
As such I'd recommend trying to make sure your GP is refering your or leasing with someone who is a specialist, GPs are often no more than a traige nurse. And the OP has been taking this for more than the textbook recommended time. I would hope with the NHS that qualifies him for a specalisit rather than a generalists, one of the NHS finest GPs didn't even know what the asthma drug I was taking was, and had to look it up in her reference text before now, meanwhile I'm there sitting politely as you'd imagine me, suggesting the correct dosage of Prednisolone would xxx when she was recommending almost twice too much!