IO540 thanks for the reply, it seems to confirm my belief. If MP is a method (all be it not very precise) of measuring torque then at a fixed RPM and fixed MP you'll be developing a particular power output, if the RPM is decreased then for the power output to remain constant the torque (therefor MP) has to go up (because Power (HP) = Torque (MP) * Angular speed (RPM)).
In that case this has been an informative, but slightly pointless thread as it has just confirmed what I thought, but with a better explanation than i could have given.
Cheers All
Owen