Caterpillar

I spent a lovely two hours out in the garden today tidying and starting my spring cutback. Spotted two enormous bumblebees and found this caterpillar. Possibly a White butterfly however I’m not sure I’ve any food plants for it if so. They like nettles and nasturtium and my tub of the first is in it’s infancy at the moment and I’ve only nasturtium seeds! The kittens are exhausted having been out with me all afternoon :)