There will be much written about this incident in the coming days. As someone who works in a bureaucracy I often think about the human element of this - what the hell did this man feel when he was told/briefed about the loss of these disks ?
It is difficult to know how one might feel when your staff come to you to say you are managing "an unprecedented" breach of confidentiality, and it has happened (it is suspected) because people have not followed procedures.
If only there was a camera that followed the moments when the staff thought "its only a couple of disks, throw it in the post", and what was happening in the period leading up to that result. If you could bottle the lessons, there is big money to be made in the risk management business.
But the human bit aside, it is a big political issue and the Chancellor has to get on top of it quickly.