Knowledgeable sources tell me that Brodie Clark was considered useless by many of the Border Agency staff, partially because he didn't know what he was doing. How true this is, I know not, but his popularity with the staff was pretty low.
rjc54n's analysis seems pretty accurate to me, however. The demonstrated incompetence is why I still like the idea of a public flogging of the Home Secretary every time the wait exceeds 10 minutes in the EU queue!