Steering Column Locking/unlocking Problem

Hi All

I have a 2003 x350 (XJ8 4.2 SE). I have a worsening intermittent problem with the steering column locking device either not engaging when the ignition key is removed or, recently, not releasing when the key is inserted. I don't think there is a problem with the keys (the using a different key doesn't fix it) and I don't think its the key transponder reader in the lock as all sorts of other stuff sarts working when the key is inserted and stops when it is removed - such as the driver's seat moving from the easy-access position to the driving position and back again. does anyone have any ideas?

Thanks