The CAA did a safety review in 2007 following the introduction of the new JAA rules on biennial instructor flights, 90 day rule, annual MEP tests etc which were introduced in 1999/2000.
The review concluded that they had brought no improvement in safety statistics.
I used to keep a link to the paper in my bookmarks but alas it is now redundant following the revamp of the CAA website and I can no longer find it.