My husbands ex partner changed his sons name by deed poll when he was 4. It was perfectly legal, sadly. At the time he was trying to obtain parental responsibility through the courts as they had not been married. The mother changed his name after the court had received the papers and she was held in contempt of court as apparently she should not have done it whilst there was an ongoing court case. The judge however ruled that it was a trivial matter and left it at that!!! My husband was heart broken. This happened in 1996 so not sure if things have changed. Incidently, one month ago my stepson came to live with us as his wonderful mother was sent to prison, poor kids been through hell. We have now changed his name back, at his request........patience in the end really was a virtue, good luck