@eldergarth every practice has to provide emergency appointments. Call your gp at opening time and they will ask you to either come at a certain time or come immediately and wait.
I've lived all over England and every gp practice I've had over 20yrs have that facility.
Go get it diagnosed so you know how you can help yourself!
These forums are filled with huge experience and someone will guide you, whatever the diagnosis.
The sooner you get diagnosed the more you can settle down and concentrate on your diabetes. Win win situation. Right?