"Some of the boys left to get married, settle down, form their own bands, that sort of thing," says Ian Anderson.

"Jeffrey Hammond-Hammond left to be a painter, John Glascock tragically died from heart disease, and two were fired. We are all pretty good pals now, like a big extended family of two football teams."

Keeping up with Jethro Tull's fluctuating line-up is enough of a challenge without the lengthy odes and riff-laden preposterousness which have provided the soundtrack to their 29-year career.

Beginning life in the form of four shaggy-haired dreamers from Luton in 1967, the band had already changed line-up by the time they released second album Stand Up under the leadership of flautist Anderson in 1969.

"We had many different names which usually changed every week," he rues of their early struggles. "Since we were so bad we had to pretend to be some new band in order to get rebooked in the clubs where we aspired to find fame and fortune."

Stand Up provided their only UK number one album but it is the 1971 epic Aqualung which remains the group's most revered work.

A prog-rock classic still providing essential fare for rock purists today, it illustrates why Tull provoke the widest imaginable spectrum of reactions from audiences.

Voicing strong opinions about religion, society, paedophilia and prostitution ensured Aqualung was never going to threaten easy-listening sections.

Yet, as many of their peers embark on comeback tours, the part-time fish farmer insists the band are revisiting their most famous piece rather than attempting a half-baked reunion.

"Tull have never disbanded, not even for a minute," Anderson says. "No comeback tours for us, thank you very much."

He also puts the longevity of the band down to the devotion of their supporters.

"Committed fans ensure the work of bands like Zeppelin, The Grateful Dead, Hendrix and the Stones won't fade away," he declares.

"Tull is just a lesser version of those rock giants whose music will go on to define the form in the history books of the future."