A former Army general who was known as "Rambo" by his men seemed an unlikely reformer and troublemaker. But more than a year on Michael Howard must be beginning to wonder if he made a horrible mistake.
Today sees the latest in a series of inspections that spectacularly draws attention to shortcomings in the Prison Service. Not only has Sir David, 62, become increasingly confident about speaking out against what he believes are "unacceptable" conditions at individual jails, but also he is starting to campaign on several penal issues.
His growing willingness to become involved in potential areas of policy has infuriated Mr Howard and his officials. Within weeks of his appointment in December 1995 he marched his inspectors out of Holloway women's jail in north London in an unprecedented act of protest. It was the start of a campaign for better conditions for women prisoners.
His latest area of interest is the state of juveniles in jail and the corruption of young offenders. His is about to set up an inquiry into this subject and has called for new specialist prison directors to be appointed to examine the problems of young offenders and women.
He is pushing for changes to the way inspectors' reports are published so that they are removed from the control of the Home Secretary. He has also criticised "boot camps" and made himself very unpopular with ministers and officials by suggesting that his job should cover the Prison Service rather than just the inspection of prisons.