I have a triton jade ii shower and although its hot enough the water pressure is rubbish, I've changed the shower head but this makes no difference, the bath and sink in the room are ace any ideas?

You are going to have to disassemble the valves until you find the restriction. There's no other way to find the problem. Turn off water first.

I found a manual here: http://dl.dropbox.com/u/8010163/jade3.pdf
I would check the inlet filter and the solenoid. Probably scale has stopped something up. Make sure to turn off power and water first.