Don't know how that happened. Penge is pen coed, the head of the wood, ie the Great North Wood in the north of Surrey, now Sarf Lund'n. There's still a little bit of it left, but it is currently being decapitated as Bromley cuts the trees on the top of the Crystal Palace ridge preparatory to building a glass fronted multiplex. One of my place-name books points out that Celtic names are sparce in the east, but adds that while Sussex has none, others such as Essex have a few, Kent has several. The only example is Dover, as above. Still looking. There is Kent itself, recorded in that Greek explorer who circumnavigated these parts. I'm surprised that the river Adur in Sussex is not supposed to be a Celtic name.