Right, final thanks to everybody for their help; everything now working beautifully, just have to shuffle the huge wiring harness into place in the daylight in order to be able to secure the head unit in the dash.
Turns out the microphone wire was the least of my problems!
For what it's worth i secured the mike into the headlining of the panel that hides the sunroof motor and then ran the wire inside the headlining and down the inside of the A pillar trim and through the fusebox and finally under the steering column...