Hi Rockhopper & thanks for the advice:
24hrs after disconnecting the Optimate the multimeter battery reading was 13.02v. Switching the Datatool off then turning the ignition key to the 'on' position (as usual got relay click but no pump whirr) the reading went down to 12.82v, then pressing the starter button for 5 secs gave a reading of 12.30v. When the key was turned back to 'off' the level crept back up to 12.90v.
I've rechecked all the fuses, and can''t find any loose or damaged connections..Sorry to keep asking for help,but if anyone's got any suggestions then I'd be very grateful!
Cheers, il.