Managed to get the job done this afternoon.
Spliced in the wires for the earth, ignition live and permanent live, and all working nicely.
The next decision was where to mount the parrot's head unit. I tried a few places, and my initial plan was to mount it on the front of the two blank switch plates below the fog light switches. However, once fitted it just didnt look right, so I moved it a little bit lower:
It now sits to the left of the steering column, and is visible when driving but not distracting. My phone sits on the dashboard in a holder anyway so realistically I dont need to be able to see the screen on the parrot to see who is calling. It's mounted using velcro so can easily be unstuck (which is necessary to open the access panel below the steering wheel)
The microphone wire was then fed out through the side of the dash (theres plenty of space to feed a cable) and up the A-pillar trim, emerging at the top. The microphone is actually just wedged in place:
All tested and working. It would have been simpler if the person i bought the parrot kit off hadn't hacked the wires about as it would have just been plug and play - although there'd have been even more plugs to fit in the space behind the radio head unit!!
I also discovered today just how many sharp edges there are on the back of the dashboard to slice hands open on when feeding cables!!
For anyone thinking of fitting a similar kit, it was pretty simple. The lack of an aux in on the radio isn't a problem as the parrot's control box actually sits between the radio and the speakers, and simply mutes the radio audio and inputs its own audio when in use. The only issue i've found so far is that the amp presumably gets its power from the radio, and therefore only works when the radio is on. Thus if the radio is off, there is no sound from the parrot to the speakers! Can't think of any easy way to solve this though.