Over three decades after its relase, Pink Floyd's "The Dark Side of the Moon" remains one of the most acclaimed albums of all time. Its sales total around 30 million copies worldwide, and it continues to sell 250 000 copies a year. In its first run, it took up residence in the US charts for a mind-boggling 724 weeks, according to recent estimates, one in five British households owns a copy.

But, as John Harris's unofficial account reveals, this is only a fraction of the story...