Common Blue Butterfly Polyommatus icarus

Common blue topside
Common blue underside
The Common Blue Butterfly is common over much of temperate Eurasia and is the most common of the several blue butterflies in the UK. Only the male topside is mainly blue.
blue butterfly top
blue butterfly side
The beautiful Common Blue butterfly, male -- Totteridge Fields, North London
Male Common Blue
Male Blue butterfly
Another male Common Blue
Common Blue female
Common Blue butterfly female
The female Common Blue usually has some blue scales, particularly near the body, but not always, - can be quite brown.
Common Blue butterfly female
Female Common Blue
Female Blue butterfly
The female Common Blue topside - brown with orange spots - can look similar to the Brown Argus, but the Brown Argus female has a full set of orange "lunes" on the forewing, unlike Common Blue (and male Argus).
Common Blue butterfly female
Female Common Blue
Female Blue butterfly
The underside is also similar to the Brown Argus but has an extra spot on the forewing (circled yellow) and two spots more distant from each other on the hindwing (circled orange).