Bright orange with a sky-blue, dotted border and tiger-striped shoulders. The tattiest Small Tortoiseshell butterflies are usually seem early in the year, as early as February, having emerged from hibernation and the freshest individuals are often late in the year (October/November) having emerged from their chrysalis to feed up for hibernation.
With closed wings, the Small Tortoiseshell butterfly is well-camouflaged as a dead leaf.
It's relative, the Large Tortoiseshell is extinct in the UK but rarely appears as a migrant from continental Europe.
The Scarce (Yellow-legged) Tortoiseshell is from East Europe/Asia (see link below).
SMALL TORTOISESHELL CATERPILLAR:
Like Peacock butterfly caterpillars, Small Tortoiseshell caterpillars live their early life en masse in a silk web and feed on nettles. Both are at risk from parasitic flies/wasps.