Here are some images taken yesterday at Murton Green showing early and late stage mines and another type of similar-looking leaf browning.
early stage mine
late stage mine
leaf damage mimicing mine (note darker edges and lack of crescentic marks of real mines where larva has been feeding)http://www.ukmoths.org.uk/show.php?id=2900. The map below, shows the recorded distribution in Glamorgan to date: