Ian, it's a little hard to tell from your picture exactly what species of shark teeth these are but by their relative shape and size they appear to be types of Carcharhinus teeth.  Recommend a great website for tooth identification: go to www.elasmo.com, then select Lee Creek, and then click on the Sharks-II link.  Scroll down a little ways until you see the several different species of Carcharhinus sharks (Copper, Dusky, Silky, Bull, etc.) listed.  Also check out the hammerhead teeth near the bottom of that same page.  Overall elasmo is a great site for tooth ID help, especially if you don't have any fossil books on hand.

Since you were an avid metal detector hunter, it would interesting to see pics of any neat/interesting stuff you may have found.  You could post in the artifacts area or wherever.

Daryl.