Cheers for the replies. Nipped into Halfords and tried another harness but still no good. The lad there said that a piggyback off the fuse box is the easiest way, like @dezwez said.
Is it as simple as fitting one of these: http://www.ebay.co.u...=item27bf1644ed
to something like the electric windows fuse, then running the wire to the red of the stereo?