I live just a few miles away from Finedon Dandy and have also had the small mauve/pale blue butterflies fluttering through the garden during the past week or so. I am no expert on butterfly recognition and at no time did one settle long enough to take a close look. I checked butterfly sites on the net and thought they might be common blues but it now seems likely that they are in fact holly blues looking at other posts on this thread. Nice to see them around in any case.