I posted about my mother in law a few months back here.
In addition to the changes in her behaviour over time, we've become aware that her confidence and ability behind the wheel has become compromised. She apparently won't now drive after dark, as she cannot judge distances or speed very well, despite having regular sight tests. She also refuses to drive anywhere she doesn't know extremely well and refuses to detour onto any route if she's even the slightest but unhappy about the conditions or road layout. Apparently her driving has lately become quite erratic, specifically with regard to her situational and spatial awareness.
My partner and I strongly suspect that she's suffering from the symptoms of vascular dementia, however in recent months she's cut off all contact with us and we're in no position to talk her out of driving.
Basically, what's the procedure here - do we contact the DVLA directly or should we trust that our GP has the matter in hand as we've already expressed our concerns to him? The DVLA states that it's the responsibility of the driver to declare any medical conditions which may impair driving, however given my mother in law's stubbornness, I can't see her doing this voluntarily, even if she was aware that she has a condition.