Bristol GS is an excellent course, but provides a theory course for ATPL(H) level exams. The other courses mentioned in this thread are for CPL(H) level theory, which is quite different.
In simple terms, there is not really much point in obtaining ATPL(H) exam credits if you are not intending to take your Instrument Rating, IR(H), within 3 years of passing the exams, otherwise you more or less have to start again, as the ATPL(H) theory credits actually have an expiry date.
The only other advice I can give is that the ATPL(H) theory is much more in-depth study (very intensive) and will take about twice as long to complete as the CPL(H) theory.
Hope this helps...