Changing names.

I am looking after a 10 year old boy who is in long term care with me. When he came to live with us he asked if he could change his first name unofficially as he associated his real name with some really bad memories. Social services agreed and he has never looked back. Nobody ever refers to his old name, indeed a lot of his friends know nothing about it and if a letter or document slips through the net he becomes very distressed.
He is now asking if this can be done officially so that doctors, passport and in the future any exam certificates will be in his preferred name. I know that if he wasn't looked after he would be able to do this legally when he is 16/17. The LA say they have never heard of this before and are unsure how to proceed ( they have parental responsibility).
Can anybody point me in the right direction? It would be so sad for this young person in the future to be reminded constantly of their past. Naturally if they are not allowed to change their name legally all certificates will be in their old name and therefore I imagine any job applications will have to be the same to tie in with the certificates.