The deed's been done. I officially pollinated (hopefully) the two plants this morning before any full sun was able to shine on them.
I used a small artists paintbrush to gently apply pollen from a Barneys Farm Red diesel Clone which had been feminised using a sodium thiosulfate solution.
See https://growdiaries.com/diaries/42051-barney-039-s-farm-red-diesel-grow-journal-by-grey-wolf-growdiaries for those details .
Time will now tell whether I was successful or not.
@Pointlessmike, I used a sodium thiosulfate solution which I made up from mixing sodium thiosulfate with silver nitrate and then diluting and spraying on the chosen receiving plant or clone