It was originally released as just "Halcyon", which was a slightly longer mix and a little less clubby. The name comes from their mother's struggle with the medicinal tranquilizer 'Halcion', which is reflected in the music video:
It samples Opus III (vocalist: Kirsty Hawkshaw) - Fine Day, which had made it to #5 in the UK charts the previous year. They played the "la la la..." vocals backwards to make Halcyon. When they perform the track live, Orbital have a habit of playing additional samples of Belinda Carlisle - Heaven Is A Place On Earth and Bon Jovi - You Give Love A Bad Name on top: