"Not Forgotten" is the first single released under the Leftfield name; however, Paul Daley was not involved in the song's creation. The song was written by Neil Barnes and released only on 12" in 1990 on the Outer Rhythm record label, published by Rhythm King Music.
Electronic music magazine Mixmag praised the single as an important step forward for British house music. The magazine stated that "If any one record could be said to be responsible for finally making British house more respectable than its American and European cousins, 'Not Forgotten' was it. No longer would British house heads be constantly looking over their shoulders at New York, Ghent, Milan and Berlin. 'Not Forgotten' and subsequent Leftfield classics like 'Release The Pressure' and 'Song Of Life' were the cement that welded a whole new British house scene together. London proudly joined the league of house capitals. British dance music has never looked back."