Apologies if you've heard any of this before. My diagnostic route began September 2008 at my GP's. He got me to do a few very basic tests and listened to my description of the symptoms. He arranged an appointment to see the Neurologist.
Saw Neuro November 2008. He put me through various physical tests etc. He explained that there was no single test for PD, it, in most cases, means ruling out other possibilities and basically seeing what's left. He reckoned it was PD from the start, but to be certain I had blood tests for all sorts of things, an MRI scan and a deep look into my by the eye consultant looking for any signs of Wilson's disease. I also started on Sinemet+ 125mg, 3 per day.
The Sinemet+ did make a clear improvement in controlling the symptoms, that combined with all of test results left us firmly with diagnosis of PD in June 2008.
In terms of the delays you're experiencing, if you know which hospital the GP is referring you to you've nothing to lose by contacting their Neurology dept/outpatients dept direct and asking a few questions.
The results from any test should not reduce the rate of progress towards a diagnosis.
Hope this helps, if not feel free to come back for more.