Rare wood white? or common cabbage?

I'm unsure if this is a rare wood white butterfly, or just a common or garden cabbage white. Surely there are some grumpy gardeners (or lively lepidopterologists) who can put me right? Either way, after a long day of studying rather dry management theory, it was lovely to watch it dancing over the flowers and nettles by the river this evening, so it's special to me.