Silbury Air by Harrison Paul Birtwistle (1934-) is a composition for chamber ensemble. The piece was written in 1977 and revised in 2003. The premiere was given at the Queen Elizabeth Hall on 9th March 1977 and the piece performed again at this year's Proms at the Royal Albert Hall.
Part 1 here - http://www.youtube.com/watch?v=Pnllf6XVhJI
Part 2 here - http://www.youtube.com/watch?v=S2XRMuvisCo&feature=related