Cleaning round the inside with the vacuum cleaner today I found what I thought to be a button for releasing the trim panel under the steering column, in the driverside footwell.
I pressed and pressed and nothing happened.............. then I pressed slightly differently and the button turned out to be a tiny 2 piece louvre about 30mm long and 10mm wide. Turning the key in the ignition started the climate control .............. and now I can refrigerated knees, it is a tiny footwell vent! There isn't one on the passenger side (maybe on HSE and S/C models!!) Rear passengers recently have commented on how much better the rear aircon is compared to the RR system.

The disco 3 has one of these as well i believe. Its out there somewhere. Second V10 Treg on the drive at the moment.