Ok, so all power connections sanded down and shiny, fuses checked visually and with multimeter, red key used but no joy. The only slight signs of life I've noticed are a click from a power relay I believe to be aftermarket (heated grips, extra power socket etc run off of it) and there seems to be another small click from the clocks/display when the ignition is turned on, otherwise nothing, not even an immobiliser led flash.

When I said before I'd changed the main relay I cocked up and it wasn't the main(?) 5VK-81950-40 relay assembly but the power relay I heard click. If the 5VK relay (or any relay for that matter) had somehow gone pop would it result in the symptoms I have?