I & few others I know have recently converted to the UK ATPL or CPL. Not JAR but it might give you an indication of what to expect. The general perception seems to be that JAR is just the same only longer, more difficult, more expensive & with more traps in it!
With an Oz or NZ ATPL & IR we were given a credit for the morse code exam that is part of the technical group, were granted a flight radio telephone operators licence without a separate test & had no minimum number of flight hours required ie whatever got us through.
All up we had to do all exams in the navigation group (8) + all except morse in the technical group (6) + Perf A (1). We could have done Perf A in the tech. group however the requirements to gain at least a PARTIAL pass (ie pass 50% of the exams in that group) made it a lower risk to sit Perf E in the this group.
If at least 50% of either group exams isn't passed in a sitting then you must sit the ENTIRE group again! Hence the Perf E instead of Perf A to improve the chances. A benefit from the morse credit is that it reduced the minimum exam passes for a partial from 4 out of 7 exams to 3 out of 6. ie one less opportunity to screw up.
The morse credit is only given if you hold a current instrument rating.
On the flying side it took me 6 hrs of training + 3.5 hrs of flight tests (A 'GFT' for the initial issue of a UK professional licence & an IRT). I also hired an ATC-710 for 2 hrs before going to do the flying.
My background is all GA, but with experience as CFI of a multi/instrument/instructor & aerobatic flying school, & about 3700 hr TT. I feel my instructional background helped as the test was in a Seneca 2 & I have a couple of hundred hr instructing in these.
Hope this helps.
T