Is it a Common Blue leaving a pupa or is it a snail attaching itself to the butterfly
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That is an excellent and rare picture Lipper.
I don't think (I am pretty certain) that is no snail.
This looks like a sad case of a butterfly not having succeeded in emerging fully from the pupa, with the result that the left-hand wings have not expanded fully.
Lat/Lng: 52.364, -6.3713
OS grid ref: SM025829