I have a 1 yo pet budgie, he is kept on his own, with plenty of toys
(including a mirror) in a good sized, regularly cleaned cage. He
also loves being out of the cage and following me around the house.

He is forever preening himself and the like, he seems to be most
irritated around the nape and throat, he loves being rubbed in these
areas and has a couple of bald patches. He also has chewed and
ruined a couple of large feathers on either wing.

I have taken him to the vets, who could see no sign of parasites or
anything like that but he still persists in scratching himself and I
have also noticed what I can only describe as dandruff coming off
when rubbing it.

Has anyone idea what is causing this??