Thanks for the replies so far.
Yep, I realise I won't be able to earn money by virtue of only having a PPL. If I get the "knowledge" (sound like a Lahn-dan cab driver there) done, I'll probably do the CPL somewhere down the line. I'm a fixed wing person too at the moment, so I appreciate that the rotary CPL requirements differ from those needed for us plank drivers.
It's just that I want to be able to fly with my mates here in the UK and legally give them tuition and log the time. Or, possibly fly for free giving instruction in my spare time. As it stands, I did a load of good quality training at a proper stick and rudder school out in the States, have knowledge to impart, and don't want to get rusty. Also, when friends need BFR's for their 61.75 (based on) FAA Private cert's, we'll be able to do that properly.
The hours I've got exceed the 150/200, and I'm aware of what's required for the FI rating, and look forward to learning how to instruct the JAA way. So I just need to know about the "theoretical knowledge" aspects. I honestly can't be fussed (almost said something else there) having to do the ATPL's, but it looks like I'll have to do a similar thing anyway, having to enrol with a school, pay daft amounts of money, go to a CAA testing centre etc etc.
Am I right in thinking that there IS a different set of CPL exams (possibly same questions involved) then? Does anyone do these any more, or are most people future ATPL-ers and do the whole shaboodle?!