Robin Harper said he wouldn't change image for Holyrood

In his autobiography, to be published next week, he said after he was elected to the Scottish Parliament in 1999, some people argued his rainbow scarf and black fedora hat were "too Green" and "too juvenile".

They wanted a "more business-like profile" and urged him to wear conventional suits and sober-coloured ties.

He wrote: "I resisted because my scarf, hat and tie foible gave the party instant public recognition. Indeed, people quickly began to complain to me if I turned up at events without them."

Mr Harper, 70, who made history as Britain's first Green parliamentarian, described how he was inspired to join what was then known as the Ecology Party in 1985 after the sinking of Greenpeace's Rainbow Warrior. But when he contacted the party's Edinburgh branch, they asked to hold their annual general meeting in his flat and immediately elected him secretary and convener.

He stood in 11 elections - Westminster, European and council - before becoming an MSP and says he was "in a complete haze" when he realised he had won.

After four years as his party's sole MSP, he was re-elected in 2003 as one of seven Greens. He wrote: "We had sprung the trap of being just the cuddly Robin Harper Green Party and had been recognised as serious players."

The Greens were then given time at First Minister's Questions, but Mr Harper confessed he was never at ease with the task. "I hated the preparatory sessions with team members who wanted me to work myself up into some kind of phoney angry lather concerning issues I wanted to deal with calmly and rationally and with dignity."

The book, Dear Mr Harper, describes a childhood in Orkney, Sri Lanka, London, Somerset and Lossiemouth, as the family moved around with his father's job in the navy.

It reveals how Mr Harper discovered at the age of 49 that he had an unknown older brother, the result of an affair his mother had before she was married. The boy had been adopted but got in touch, leading to a happy reunion.

Mr Harper described how in 1965 he was on the same bill at a London folk club as "a 24-year-old American singer" who turned out to be Paul Simon.

Mr Harper sang for him a version of Scarborough Fair. "He had never heard it before, but within two years he and Art Garfunkel had recorded it as part of the soundtrack of The Graduate. The film helped make Scarborough Fair perhaps the most widely heard folk song of all time."

As a teacher at Boroughmuir, Mr Harper invited the Bay City Rollers to play for the pupils. "I gave one of the Rollers a lesson in folk finger-style guitar work because, in spite of their fame and success, they had only basic rock-style guitar techniques."

He also described how at one stage he gave up teaching to become an actor, but admitted his stage career added up to just 11 weeks of paid work.

He returned to the classroom and taught for 30 years before becoming an MSP.

Robin Harper will read from his book at Blackwell's, South Bridge, on March 30 at 6.30pm.