A familiar face, the Green-veined white (Pieris napi) here on Dame’s rocket (Hesperis matronalis).
The spot near the top edge of the hind wing make this a 2nd generation specimen [1]. Based on the visible grey coloration on the front wing tip and base, this could be a female.
Literature
1 Tolman, Tom & Lewington, Richard. "De nieuwe vlindergids, 450 soorten dagvlinders van Europa en Noordwest-Afrika", Tirion