This is indeed a large task; on UKDivers.com I spent many many hours writing a UK Wreck Database in ASP and still to date have not finished the map.
What it needs now is some input from divers. You can find it here;
<a href="http://ukdivers.com/wrecks/list.asp
I" target="_blank">
http://ukdivers.com/wrecks/list.asp
I</a> am quite happy to share the code with YD if some one wants to adapt it to include all UK Dive Sites.