A long-lost demo of the Sex Pistols‘ controversial track “Belsen Was a Gas” has emerged online – watch it above.

The track, about the Nazi concentration camp, was written by Sid Vicious prior to him joining the band. With added input from Johnny Rotten, it became part of the band’s live set from 1977. However, only live versions and a post-Rotten 1978 recording with Ronnie Biggs on vocal had previously existed.

The band have since played the track on live shows – including at festival appearances throughout summer 2008 – where Lydon updated the track as a protest to the US and UK’s invasion of Iraq, renaming it “Baghdad Was A Blast”.

The demo was recorded at the Pistols Denmark Street rehearsal room by their soundman John ‘Boogie’ Tiberi on a TEAC four-track. “John decided to work on ‘Belsen’ with Sid, rearranging the lyrics while Steve and Paul worked on the track and I wired up Denmark Street to put it down to a four-track,” he remembers.

Tiberi added: “It really shouldn’t have to be said but that’s Sid on bass. It was very clumsy, no monitors, sound insulation was non-existent. I think they all enjoyed doing it outside of the Wessex environment, which had by then become quite oppressive. When I played it to [Pistols producer] Chris Thomas he probably thought I was barmy and couldn’t understand the reverb vocal, but that’s the way John wanted it. I thought it was good as a kind of sketch idea.”

The demo was through lost but has now been restored and will feature on the box set deluxe reissue of the band’s seminal album Never Mind The Bollocks, Here’s The Sex Pistols on September 24 to celebrate its 35th anniversary.