I got my 2011 Clubman over the weekend, and found that they now have a little plastic ring around the headrest post that keeps them from being completely lowered. I understand that this is safer for adult passengers in the event of an accident, but I rarely have backseat passengers and they were partially blocking my view out the rear windows.
Removing them was super easy though. It is just a plastic ring with a little metal pin to hold it in place. I simply removed the headrest and used a tiny screwdriver to push the metal pin out. The plastic ring then slipped off quite easily! Although, before you do this, make sure to have a cleaning wipe on hand as one of my headrests was generously oiled and dripped a bit.