According to Lasors 2007:
The holder of a JAR-FLC CPL(H) and IR(H) satisfies the knowledge requirements for the issue of an ATPL(H).
So I would say if you've got a JAR CPL(H) just the 7 IR exams need to be taken not the entire set of 13 ATPL(H) exams. Remember though that you need other things to get that ATPL(H) license with your name on including obviously getting your IR(H) Rating, completing an Approved Multi-Crew Co-operation Course (if doing it this way) and meeting the flying experience requirements (check Lasors). Then taking an ATPLH test!
Caveat: I do not speak from experience; the above is just my interpretation of reading Lasors so don't take it as gospel. I am happy to stand corrected.