Hi,
To belp with id can you tell us what the colours actually are.
It looks like green with a white trace, but you're saying it's an ignition feed which would be white with a green trace.
Purple is obviously permanent.
The other looks like a red with green trace which would be side lights or indicators if it's green/red...
Cheers 
Hi Bat, thanks for your input. Looks like my Harnesses and Haynes disagrees with your colour I.D, both diagrams and my harnesses have a LG/W feed to the ignition, rather than the opposite that you suggest. On this particular diagram you can see where the LG/W does split off, and although not pictured, this single wire goes to a radio (if fitted) though it doesn't explain the other two wires.
Part labelled '35' is the ignition barrel:

Purple is indeed permanent. And the R/G cable is - as you suggest- pointing towards the side light circuit.

Here you can see the spur of the LG/W coming out the back of the lower plug and then doubling back to go to my mystery plug (you will notice I have had to repair this cable with some DG/W as the cable was severely damaged, i assume from removal of the harness)
So it seems to me we have a Permanent live, a switched live, and a possible illumination link. Sure sounds like it might be nothing more than a Radio plug to me!!
Thanks for the comments so far chaps.