[1] Following Palmer's early departure, Williamson and Heron continued as a duo and were eventually augmented by other musicians such as Licorice McKechnie, Rose Simpson, and Malcolm Le Maistre.

The band built a considerable following in the British 1960s counterculture, notably with their albums The 5000 Spirits or the Layers of the Onion (1967), The Hangman's Beautiful Daughter (1968), and Wee Tam and the Big Huge (1968).

In 1963, acoustic musicians Robin Williamson and Clive Palmer began performing together as a traditional folk duo in Edinburgh, particularly at a weekly club run by Archie Fisher in the Crown Bar which also regularly featured Bert Jansch.

It was released in Britain and the United States and consisted mostly of self-penned material in solo, duo and trio formats, showcasing their playing on a variety of instruments.

However, when Williamson returned after running out of money, laden with Moroccan instruments (including a gimbri, which was much later eaten by rats), he and Heron reformed the band as a duo.

Joe Boyd became the group's manager as well as producer and secured a place for them at the Newport Folk Festival, on a bill with Joni Mitchell and Leonard Cohen.

"[4] In July, they released their second album, The 5000 Spirits or the Layers of the Onion, accompanied by Pentangle's Danny Thompson on double bass and Licorice on vocals and percussion.

Williamson and Heron in this album had added their girlfriends, Licorice McKechnie and Rose Simpson, to the band to contribute additional vocals and various instruments, including organ, guitar and percussion.

They left behind their folk club origins and embarked on a nationwide tour, incorporating a critically acclaimed appearance at the London Royal Festival Hall.

Later in the year, they performed at the Royal Albert Hall, at open-air festivals, and at prestigious rock venues, such as the Fillmore auditoriums in San Francisco and New York.

After their appearance at the Fillmore East in New York, they were introduced to the practice of Scientology by David Simons (aka "Rex Rakish" and "Bruno Wolfe", once of Jim Kweskin's Jug Band).

Joe Boyd, in his book White Bicycles: Making Music in the 1960s and elsewhere,[9] described how he was inadvertently responsible for their "conversion" when he introduced the band to Simons, who, having become a Scientologist, persuaded them to enrol in his absence.

[citation needed] Their November 1968 album Wee Tam and the Big Huge, recorded before the US trip, was musically less experimental and lush than Hangman's but conceptually even more avant-garde, a full-on engagement with the themes of mythology, religion, awareness and identity.

Williamson's otherworldly songs and vision dominate the album, though Heron's more grounded tracks are also among his very best, and the contrast between the two perspectives gives the record its uniquely dynamic interplay between a sensual experience of life and a quest for metaphysical meaning.

At this time, most of the group lived communally at a farmhouse near Newport, in Pembrokeshire, Wales, where they developed ideas for mixed media experiments with Malcolm Le Maistre and other members of David Medalla's Exploding Galaxy troupe and the Leonard Halliwell Quartet.

Originally planned for BBC TV's arts programme Omnibus, it featured documentary footage and a fantasy sequence, 'The Pirate and the Crystal Ball', illustrating their attempt at an idyllic communal lifestyle.

In addition to the spectacle of their exotic instruments and colourful stage costumes, their concerts sometimes featured poems, surreal sketches and dancers, all in the homegrown, non-showbiz style characteristic of the hippie era.

In 1970, Robin Williamson (with little input from Heron) attempted to fuse the music with his theatrical fantasies in a quixotic multimedia spectacular at London's Roundhouse called "U", which he envisaged as "a surreal parable in dance and song".

Mike Heron took time out to record a well-received solo album, Smiling Men with Bad Reputations, which, in contrast to the ISB's self-contained productions, featured a host of session guests, among them Pete Townshend, Ronnie Lane, Keith Moon, John Cale and Richard Thompson.

The following year, Licorice left, and was replaced by Gerard Dott, an Edinburgh jazz musician and friend of both Heron and Williamson who had contributed to Smiling Men.

Notable in this output are the Grammy-nominated Wheel of Fortune (1995, with John Renbourn) and four records on the jazz/classical/avant-garde ECM label: The Seed-at-Zero (2000), Skirting the River Road (2002), The Iron Stone (2006), and Trusting in the Rising Light (2014).

Stylistically the ISB were centred around the idioms of conventional folk and pop, but their notable experimentation with musical form, instrumentation and styles (e.g. Indian and Moroccan) led them to innovative, often eclectic, compositions.

[citation needed] Both Mike Heron and Robin Williamson would insert seemingly unrelated sections in their songs in a way that has been described as "always surprising, laughably inventive, lyrically prodigious".

[15] In 2003, the Archbishop of Canterbury, Rowan Williams, who had previously chosen "The Hedgehog's Song" when he appeared on Desert Island Discs, wrote a foreword for a full-length book about the band, describing them as "holy".