I have put cones out, in the pattern as defined in the "Safety at Street Works" book, but an inspector has told me I haven't used the right cones.

The "Safety at Street Works" book and the law require that the cones have reflective sleeves that comply with EN13422, the European Standard.

If you did have cones that were made to these standards, then it may have been that the sleeves were too dirty for the reflective to work correctly.