Thanks for commenting guys
Nick - have a look at this:
http://www.talkphotography.co.uk/forums/showthread.php?t=208624
Ash uses roughly the same set up as me. The only real difference is that he is manually doing the drops wheras I am now using a CameraAxe. My settings are 50D with 100mm f2.8 @1sec f22 iso200 2x 550ex at 1/16 gelled and behind the drops.
HTH!