Eff Oh - I think we only have grandfather rights if we have the licence in the first place, ie you can't get a JAA ATPL with CAA CPL. Sadly! But thanks for the pointer to the CAA website, I haven't been there for a while and they've added a lot of useful gen.
P_s - I'm asking whether I _need_ to hour-build (dull dull dull) to get the ATPL, or am I wasting my time when a CPL will be employable in a few years' time. I'm unlikely to get (m)any multi hours in the next 7 years, so the rolling upgrade thingy with a JAR CPL won't help. Boo. As for the CAA's changes, they've left us all upset at some time or another, I'm sure!
MF55 - I wake up in a cold sweat from the calculation_nightmare most nights! I'm going to be somewhere between 200 and 250 hours short, so as you say it is do-able.
Thanks for your help guys, I'll press on for the meanwhile then. Good luck with your own licencing demons!