Flying flick,
Yes, you'll have to do the ATPL subjects again in JAA land (specifically UK, not famil with other regulatory authorities).
In JAA land, you don't have to do the CPL subjects or the IR subjects
IF you do the 14 ATPL subjects.
The source documents can be found online but it is a serious read, look up LASORS at the CAA SRG (UK) and for specific JAA/JAR stuff, go to
www.jaa.nl You'll be amused and confused for hours.