"Verbal consent of paralysed woman not accepted"

I am appalled that an consultant in a UK hospital does not know what is legally acceptable in terms of consent. My mum had been waiting to have her suprapubic catheter really inserted for over 3.months now due to their own internal.delays only to turn up on the day and be sent refused the operation as they would not accept her verbal consent for the op - my mum is paralysed from the neck down but has capacity and full understanding but they insisted they cannot go ahead without written consent, which is not only legally incorrect but also disability discrimination! Absolutely disgraced.