Hi Alex, yes I got your PM thanks, the Dartford warbler is quite a difficult bird to see as they stay mainly hidden in the undergrowth, as I said my mate saw three the other day, but he'd been looking for them on the Gower for over two years.
The best time to see them are in the Spring when the male emerges to the top branches to sing and attrack a mate, anyway as I said earlier good luck and I might see you down there as I have'nt seen one myself yet.