Roxy Music first recorded Grey Lagoons in 1971 but left it off their debut album a year later, only to re-record it for their second.

Whenever an old demo of a much loved tune is unearthed, fans rush to sing its praises. Even though it’s often pretty ropey. The main interest is historical curiosity, and in many cases the listeners’ astonishment to discover how that turd could be polished into solid gold.

Such is the case, for me at least, with this 1971 demo of Blue Lagoons, recorded a full year before they had that astonishing hit single, Virginia Plain.

One of the first songs Bryan Ferry wrote, it was left off their debut album, then revived (initially under the title The Bogus Man, Part 2) for a BBC In Concert recording, and finally re-recorded for Roxy’s sublime second album, For Your Pleasure, in 1973.

That was one of the formative albums in my life, and I remember being obsessed with Roxy after seeing them sing Virginia Plain on Top of the Pops, while most of my school friends were listening to ELP and Yes.

I’m not sure I would have been quite such a fan if this had been my introduction – though it is remarkable to think they were making music like this in 1971, at a time when the biggest hits of the day included Knock Three Times and Chirpy Chirpy Cheep Cheep.

The recording and mixing are not great – the backing vocals and bass are intrusively loud, and drummer Paul Thompson sounds as if he’s bashing tin cans.

The highlights, apart from Ferry’s theatrical vocal gymnastics, are Andy Mackay’s sax solo and Phil Manzanera’s gloriously skronky guitar solo, though it sorely misses Ferry’s piano from the finished version.

If it serves no other purpose after 55 years, it demonstrates the brilliance of Chris Thomas’s production on the final album. And the utter uniqueness of Roxy Music, especially in those early years.