I don't know of anything dedicated solely to what you are wanting. There are several fine books that speak about where in the water there 'should' be the targets a detectorist seeks.
Clive James Clynick (cjc) has a recent book, "Pulsepower":Finding Gold at the Shore with a Pulse Induction Metal Detector. On page 44 a section begins that is dedicated about where to look and illustrates various beach conditions one should identify. That portion of the book ends on page 66.
cjc has two other books published specifically about water hunting. They are, Finding Gold, Silver, and Coins with the Minelab Soverieign and Excalibur, and Advanced methods for finding gold in the water with the Minelabe Excalibur. Both those books contain information about where one should look on a beach for pirates treasure.
That being said, I don't have a clue about how it correlates with hunting on UK beaches/water. It would also be useful to browse this section of Find Mall and look at the videos and pictures others have posted while hunting. There's some clues there where one might look. Just yesterday I saw a few posts talking about what search patterns people used when hitting a beach. Do some of that reading and it'll move you up a notch or two on increasing the potential of your finds.
A few more specifics might help folks who are willing to respond...and there should be many. Are you going to hunt wet sand, dry sand, in the water, under the water, in fresh water or in salt water? Do you already have a good scoop? What detector do you plan to use? All those things are related to what you are asking and will help others provide you with information...Jim
