Depends on what "official" means. There are a lot of Japan-based translation services for certified and/or notarised translations of documents. Have you contacted the British Embassy about the precise requirements?
Did I get on your bad side, Mike? You seem to be trying to project some hypocrisy onto me. The OP needs a professional translation service and they hadn't indicated that they had done any research on the subject. Was it the use of LMGTFY that set you off?