Problem solved! I couldn't pull the socket out but removing the centre console is fairly simple. That exposed the connections which were in place but there was no power. I then checked the fuses under the passenger side dash and surprise surprise, the 20A fuse was blown. (no idea why - probably like it since before I got the car). The lesson is, don't take what the user guide says as gospel. In my case the rear socket remained live with the blown fuse despite what it says in the book. I've no idea which fuse supplies the rear socket but that's not a problem. Just have to work it through! Shoul