This is a Vanessa atalanta butterfly, commonly known as the Red Admiral. It has brown/black wings with red/orange bands and white spots on the forewings. With the undersides moltted brown to camouflage.
This butterfly is not native to the U.K.🇬🇧, the Vanessa atalanta butterfly migrates from North America and Central Europe. However it is concidered a resident to the south due to signs of overwintering.