Usually described as a folk band or a chamber-prog outfit, they're probably closest to an orch-pop invocation of the nostalgia one might feel for the last time one saw a bird in flight and thought of nothing else. They purvey an English poetic - at once restrained and infinitely ornate, resonant and deep. In fact, their first two albums have no lyrics made up by the band, for the non-instrumental tracks are adaptations of 19th and early 20th century British poetry.
I've been listening to all of their albums obsessively. All three records are phenomenally beautiful and show a rare kind of caring thoughtfulness that brings firmly-rooted, deep-sown emotions to the surface. The first track of the playlist I'm about to link was stuck in my brain as I woke up recently and has been cropping up ever since - the very thought of it makes me to yearn for eternity.
Here is that playlist. As a final point of reference (although you won't need many, as the music exists without almost any musical zeitgeist or discourse you could name), the history of this group is inextricably linked with that of Cardiacs, the punked-up, fizzgogging, firework-eating side of the same coin.
You'll also be wanting to hear Berliner Luft, motorik as performed along a country path by a Spotted Wood butterfly:
...and here they are on Spotify: http://open.spotify.com/artist/3eyp3SryLYlr8OqCkpFQHF
I'd describe the first album as perhaps the most magical - it feels like the quietest and most mysterious of the collections, and it contains possibly the highest density of standout tracks, but they're all wondrous.