Being diagnosed with Parkinson's does not mean you will lose your driving license. Most people with Parkinson's will continue driving. However, by law you have to let the DVLA know; not to do so may invalidate your insurance. The DVLA will review your license regularly, asking for updates on your condition.
You can contact the DVLA by calling 030 0790 6806 or visiting the DVLA website.
Once you have notified the DVLA they will write to you with a form to complete and asking your permission to contact your consultant. Usually they allow you to continue driving during this process.
Your hospital consultant will provide the facts of your diagnosis of Parkinson's for the DVLA but the ultimate decision regarding your driving rests with the DVLA. In most circumstances they will allow you to continue driving but ask for a review every three years. However, if you have problems with staying alert, sleepiness, reaction times, thinking or eyesight, these may affect your driving ability. You would need to discuss these with your GP, consultant or Parkinson's nurse specialist.
Parkinson’s UK have a useful leaflet with all the information you may need to know about driving. Read: Driving and Parkinson's