My serious plant hunting got off to a good start this weekend with this stunning Lords-and-Ladies cultivar emerging from a hedge in Ben Rhydding. Arum 'Chameleon' is a relatively new cultivar, so its not one that I would expect to be planted (this plant was emerging out of the church boundary hedge) or to self-seed true to form.
The consensus seems to be that this cultivar is likely to be derived from a cross between the native Arum maculatum and the non-native Arum italicum subsp. italicum (increasingly commonly naturalised). However, no one knows for sure.