Quite grey, so first brood?
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The relatively small grey tip to the wing confirms Small White, and the strong black spots suggest female rather than male. I would have said the second brood has more grey on it than the first, and also the time of year is right for second brood (first is out in mid-April to mid-June in a normal year, if such a thing exists!).
Entomologist and biological recorder
Dear Martin, Finding the difference is much more complicated than you'd expect! My dad read a bit in Chinery that said, "dark markings much greyer in first brood" he thought that meant the wing tips, but I guess it means the spots!
Yes, explaning visual things with words can be tricky! I think you're right that Chinery must mean the spots in the first brood are paler, but the differences between male and female don't help either!
Lat/Lng: 53.465066866632, -2.2487149536937
OS grid ref: SJ835965