"Leader Records was a British folk music label, started by Bill Leader. Between 1969 and 1978, Leader released many important releases of both traditional and folk revival performers, the latter category including Nic Jones, Martin Simpson and Dick Gaughan and released on a complementary label - Trailer. Among the field recordings released on the label - often with gatefold sleeves and extensive notes in a high-quality booklet - were 'The Border Minstrel' by Billy Pigg, and 'Unto Brigg Fair' which featured cylinder recordings from the early 1900s made by Percy Grainger of Joseph Taylor and other traditional Lincolnshire singers. The 4 LP boxed set 'A Song for Every Season' by the Copper Family was also recorded by Bill Leader and released on his label."
"In the 1980s the Leader catalogue was sold to another record company which then went into receivership. Subsequently sold to Celtic Music, the vast majority of Leader records have remained unobtainable since then, with only a handful of tracks re-released on CD."
Source: http://folkopedia.efdss.org/Leader_Records, consulted on 10/01/2011. Trailer Records in the LER series are included in the list on this webpage.