Butterfly on a Buddleia

Finally managed to get a blip of a butterfly. The reason for their absence from my blips has been the fact that there just aren't any around. I have seen about two butterflies this year and that was on the golf course. However while pottering around my mother's garden this afternoon this one fluttered by and landed on the Buddleia.

I have attempted to identify it and I think it is a Green-veined white butterfly, but I could be wrong.