Diagnosis for my son

My son has always been on the spectrum but never diagnosed. Having started secondary school in a September he has experienced voices and visual disturbances often saying they are hitting or stabbing him and also telling him to hurt others and himself. Fortunately he knows not to do this and hasn’t acted on it. 

School have been very supportive and doctors have referred us to mental health services but I’m looking into how to get a private diagnosis as I think this could be the best course of action to get him the help he needs.

Does anyone have similar experience that might able to advise me?