This is a song written and performed by British electronic dance music duo Orbital, who comprise brothers Phil & Paul Hartnoll. The original form of the tune first appeared on the Radiccio EP, which peaked at #37 on the UK singles chart. It did not appear on a full-length album until the compilation Work 1989-2002, and then only in its shorter "single edit."
The song features a backmasked vocal sample by Kirsty Hawkshaw from "It's a Fine Day" by Opus III. Paul Hartnoll told the NME August 7, 2010: "The reason we sampled it was we'd said we should do a track together and never got round to it - all of a sudden they got successful with that so we thought, 'Let's bloody sample that then.'"
The song's music video was shot in the Hartnolls' home and Kirsty Hawkshaw played the mother who was "under the influence."
The Halcyon was a mythical bird similar to the kingfisher, which was said to remain tranquil during hatching and was able to calm the wind and seas. From it came the term "halcyon days," which in Greek mythology was the seven days in winter when storms never occur. The phrase is used today to describe a time of peace and happiness. Several songs have been written with the title of "Halcyon Days" (or Dayz). They include ones by …And You Will Know Us By The Trail of the Dead and Hidden In Plain View.