I would however suggest the introduction of a 13 certificate for films that are too strong for a 12 (like the Hunger Games, Chronicle, The Dark Knight), but aren't really 15 rated films...
Or offer a middle ground - i.e.
15A - 12-14 with parental accompaniment, 15+ fine on their own
18A - 15-17 with parental accompaniment, 18+ fine on their own
(i.e. an "A" would be too strong to get the next certificate down, but with aqueduct parental supervision will be okay for many in the middle ground between certificates).