The Common Blue Butterfly is as the name suggests, common in UK and can be found just about anywhere.
During the season it has two broods, one from May to June and one from July to October.
The first two images below are of a typical male of the species showing the underwings.
On the second image below, note the specific black dots which is a typical marking.
The general background colour is light brown to pale grey.
The following three images are of a typical female of the species .
Note the much darker brown on the underwings and mostly brown on the upper wings.
Also displayed are the similar black dots.
The two images below were taken by me on 20th July 2023 on a footpath on the Northern edge of Dorchester, the county town of Dorset.
When I took the shots at first, I believed it to be a female Common Blue.
Not having noticed the blue upper wings, I continued on with my walk.
However, when loading the images on the computer I noticed the blue upper wings.
I also realised that there were no black dots inward from the orange dots on the underwings.
I have sought more expert advice and initially it is considered to be a male Common Blue 'Aberration' with the sub name of Obsoleta.
I may have further information about this in due course.