Marbled White Butterfly

As the dogs leg is getting better we went for walk in the woods today for a couple of hours. This butterfly is a chalk species and the nearest chalkland where I have seen this species is 10-12 miles away. The woods are mainly clay. I suspect it has been blown by the wind as it has been windy the past few days. Its only the second time I've seen it in these woods. The last time was about 20 years ago.