Hi everyone,
Thank you for all the info, it made for some interesting reading.
I do however have some bad/puzzling news. This morning the first thing I did was check the tank to find that the leaf is clean, no sign of an egg anywhere.

The two convicts are still circling the area where the eggs were, albeit the circumference of their patrol is significantly larger and they don’t appear to be so aggressive to other tank mates. I can’t believe that another fish was able to eat them all as last night, all of them seemed to be keeping a wide distance from the eggs for fear of upsetting the parents and getting a kicking. Today I will be heading down to the shops to purchase something that resembles a cave structure in order to give them a more comfortable environment to try again next month. I will also be tracking down other convicts on show in an attempt to learn male and female identification.
Once again, thanks for all the advice and comments.
Phill.