Mysterious visitor

I had a big surprise this morning when I opened the cutlery drawer in the kitchen, a little green butterfly was sitting there! I transferred it to a cardboard box and waited until it was warmer outside then left the box in the sunshine. A little while later I went back and the butterfly had gone but a ladybird had arrived (extra), very peculiar goings on!
Having looked at the Butterfly Conservation website I think it was probably a green-veined white butterfly but if there are any experts out there, please let me know.
I wish my visitors well, hope they survive once the sun goes down.