Getting a working visa to teach in Japan

[elyar]

Hi
I currently live in London and work as an accountant. I graduated from Cambridge University last year and have been looking at teaching in Japan. I have lots and lots of teaching experience and have even been offered a teaching position in a private school in Tokyo. But my problem is that I cannot get the certificate of eligibility because I do not have a british passport. I am of Persian origin and I have an Iranian passport, but English is my mother tongue since my dad is a diplomat and I have always travelled around the world going only to English speaking schools. Can someone please tell me if there is any way I could get a working visa having such a passport. I have looked at a few other east asian countries, but Japan is the one I have my heart set on. Ideas would be very much appreciated.