Dennis Potter script discovered that casts new light on The Singing Detective

Potter, who died in 1994, began writing The Singing Detective in spring 1985. Photograph: Jane Bown

It was a little like discovering the television drama equivalent of a lost Harold Pinter or Samuel Beckett play.

An unknown script for a television play by the dramatist Dennis Potter that sheds new light on his drama The Singing Detective has been unearthed among an archive of his work in his forest homeland.