The Gatekeeper butterfly (also called Hedge Brown) is orange with a brown border and black eyespots; the male (above) has two brown "scent marks" crossing the forewing.
The female Gatekeeper doesn't have the brown scent marks. Both male and female can look similar to a Meadow Brown from above, but, unlike the Meadow Brown, the Gatekeeper almost always has two white "pupils" in the eyespot. From the side, if it has spots on the lower wing, they are always white (and the Meadow Brown always black spots).
However, rarely, some Gatekeepers have only one visible white "pupil" in one or both of their eyespots.
Female left, male right
The male is smaller and darker than the female.
Size comparison with sloe
The pair above were flying while attached,
before landing on the thistle.
Gatekeepers above were all photographed in Northwest London: Totteridge Fields, Stoneyfield and in my garden.