Well after two lots of scrubbing the print head with cloth soaked in cleaning fluid, two cleaning cycles and printing a couple of prints, I have finally cleared the print head blockage.
I used a kit called the Magic Bullet and followed a video online:
https://www.marruttusa.com/printer/support/epson-sc-p600-help.php#bullI will ensure I run a weekly nozzle check from here on, although when we might ever need to make prints for competitions again is anyone's guess.....