I think you have got one of each there, Paul! The lower is definitely small white but the upper does look very like southern. The fork is missing - a necessary but not sufficient sign - but more importantly perhaps, the scaling on the hindwing is right.
This is southern small white, taken this year:
The catepillar is spotted fritillary:
I'm off to bed now - hope I'll see a few more of your pics tomorrow!!
Guy