The Small Skipper is smaller than the Large Skipper, but difficult to tell in the field.
A more reliable way is the underneath of the tips of the antennae of the Small Skipper are orange or brown, and the Large Skipper are hooked. The similar Essex Skipper are black underneath.
The Small Skipper does not appear until some time after the Large Skipper, and is seen on the wing in July and into August.
The Small Skipper uses a variety of purple-flowered plants for nectaring and basking, e.g., Thistles, Knapweed, Marjoram, Scabious, Self-heal, and Red Clover. They'll also use some yellow flowers, such as Ragwort.