
Further, here's two pics of one of those ambiguous butterflies.
This is a reasonable guide on size as it's settled on plantain. It was maybe a little bigger than an average common blue but nowhere near as big as a large blue. Unfortunately I didn't get an upper of this individual. This is the same individual. The shot is a bit soft but the wingtip is a little crooked, presumably after recent emergence and shows black bordering where a small part of the upperside can be seen. I suspect this is one of eight or nine across the slope that looked a bit 'odd', and may be what was seen by the person who reported seeing them previously.
Any suggestions of what we actually saw?