UK butterflies

[D.P.Howson]

Our newspaper has reported many Small Tortoiseshells and Small Whites coming in from mainland Europe.
In West Yorkshire we have seen no unusual numbers of Small Whites, but the Tortoiseshells are much more numerous than is usual in late September-fourteen in the garden today, the 21st.
I never knew Small Tortoiseshells were migratory butterflies, however, can someone enlighten me?
More generally, has it been a poor year for migrants, and anyway have any unusual migrants been reported?
Turning back to this area, Commas seem much more numerous than in previous autumns, to be seen in the garden and on blackberry bushes.Five seen today, yet it is only a few years since the sighting of a Comma here was a major event-for some of us!
Dave Howson