Dazza,
It is what the job requires and not neccesarily what the post holder has. If the jobs where advertised, what qualifications and experience would be asked for.
The main problem seems to be to get an agreement with management that the experience and on job training that you have is equivalent to what is being asked for on the job profile.
You could argue that if you are already doing the job in a proper and professional manner then quite clearly you have the experience and relevant training to match the job profile. If management are arguing against this then ask them which parts of the job you are not fulfilling.