He sang shang-a-lang as he ran with the gang but all Eric Faulkner really wanted was a decent wage for all and a proper health service. The former Bay City Roller, who always wanted to be a protest singer, will appear on Glastonbury's Left Field stage tomorrow in support of Tony Benn.

Benn, appearing for the fifth time, is a big draw, but for many, the rebranding of Eric Faulkner is the more intriguing offering. The where-are-they-now stories of any band are guaranteed to interest, but in the case of Scotland's 1970s sensation, the stories have been more fascinating, and notorious, than most.

The cheery, clean-cut popsters looked so uncomplicated, from the outside. The band were formed by brothers Alan and Derek Longmuir in 1967 as The Saxons before they chose a new name, supposedly by throwing a dart into a US map.

After being discovered playing in an Edinburgh club they had their first hit in 1971 with Keep On Dancing. By 1975, they were one of the UK's most successful acts. Success in the US followed with Saturday Night in 1976. But then, partly as a result of their relentless schedule, the cracks started to show.

Compared with how he was back then, the transformation of Faulkner into a political singer in the Neil Young mould may seem incongruous - when Young was singing The Needle and the Damage Done, the Rollers were grinning through All of Me Loves All of You. But the 53-year-old says political songwriting was part of his upbringing - his father was a senior official with the Boiler Makers' Union, forerunner of the GMB.

"Even when I was in the Bay City Rollers I used to talk about issues," he says. "But it didn't fit the agenda. The record company and management just wanted the boy-next-door thing. Now I do stuff by Pete Seeger, Ewan McColl and my own songs. It's not a soap box but I want to challenge the apathy in music and help bring back the protest song."

Although engaged in a law suit to recover royalties from the Roller days, Faulkner prefers to dwell on his current music, the themes of which range from surveillance, apathy and the legacy of the collapse of heavy industry, and politics.

Not all his former band mates have such a positive tale to tell. Drummer Derek Longmuir left the band in 1981 and trained as a nurse, working at Edinburgh Royal Infirmary. He was sentenced to community service after admitting possessing child pornography yet maintains it did not belong to him.

His elder brother, Alan, the bassist, quit at the height of the band's fame in 1976 after claims he attempted suicide. He has suffered health problems, including having a stroke, and lives in Scotland with his wife. Like Faulkner, Les McKeown, who lives in England with his Japanese wife, is still involved with music, touring with Les McKeown's Legendary Bay City Rollers. In 1990 he attempted to become the UK entrant to the Eurovision Song Contest. He admitted being a drug user in 2006 but was acquitted of cocaine dealing with former Roller Pat McGlynn.

Stuart "Woody" Wood, the guitarist and later bassist, lives in Edinburgh with his wife, Denise. He is still active in the music industry, producing Celtic music, and has worked with X Factor-finalists the MacDonald Brothers.

But the most notorious figure from the Rollers' days is Tam Paton, the manager, who was fired by the band in 1979. He built up a multimillion pound real estate business based in Edinburgh. In 1982, he was convicted of gross indecency with teenage boys and served one year of a three-year jail sentence. He was convicted of supplying cannabis in 2004 and fined £200,000.

Maybe a reunion is a bad idea, then?