I'm trying to login to do my SEF online but can't remember my password and in order to get a password reminder I need to type in my e-mail, username and Ofsted Security token but I don't know what this is, does anyone know?

It's on the 2nd page of a letter Ofsted will have sent you around August / September time.

If you can't find it give the helpful guys in tech support a ring and they'll send you a new one out :D