Unfortunately....
Led to believe that there are no credits for issue here.
Just looked at this myself and my source stateside has said that yes, you need to do the FOI test, yes you have to do the oral, yes you have to do the skills test and the minimum number of hours is as stated in the FAR AIMS.
However, he pointed out that most of the applicants for the C.F.I. fail (or at least partial) the initial attempt as they're not prepared for the depth of the questioning that the examiner goes to. As an existing instructor, even though this is a JAA ticket, you should be well practiced with the patter and the exercises - and have a greater understanding of the subjects and the level of detail you'd need to explain to a PPL student.
Willing to be proved wrong. Sure someone will advise chapter and verse here.
DD