++Update++
In case this happens to anyone else, Jason & Ray from support have found the issue. Its a conflict between DA & DataTables plugin [].
From support "The jquery data table has its own sorting functionality that uses javascript and is overriding the main sort from DA in the server side code.
The two could probably be used together, but they are basically working in two different worlds. Client side javascript for the jquery and Server Side php for DA, so it would take some careful configuration to make them play nice together."
Thanks for helping me identify this issue, getting round it is another problem but at least I know now ehere the problem lies, would have taken me months to find that!
Regards
Gary