After he got back to London he accepted a place at Liverpool University to read Law and on the day he got there in 1965 bumped into Roger McGough in a bookshop.
Roberts was also recording with McGough's music/comedy outfit The Scaffold, on a series of singles which included their breakthrough hits "Thank U Very Much" and "Lily the Pink".
With The Scaffold's success McGough dropped out of the poetry gigs, leaving Roberts to suggest to Henri that all they needed was a bassist and drummer to become a bona fide band.
They also toured the United States later in 1969, on one gig in Detroit sharing the bill with Joe Cocker & The Grease Band, The Kinks, Grand Funk Railroad and The James Gang.
The band's name was picked on a whim when they randomly opened a copy of The Concise Oxford Dictionary of Music to find Plainsong at pages 450–451.
[9] The group recorded several radio sessions for the BBC and toured extensively with drummer Roger Swallow added to the line-up.
Disagreements on the direction the album should take between Matthews and Richards occurred and in the event its release never came to fruition, leading to the break-up of the band.
In 1991, some eighteen years after the original band broke up, Roberts encountered Matthews again when he was performing in a pub in Brighton, and the two decided to revive Plainsong.
Their final album as a quartet, Fat Lady Singing, recorded live in the studio, was released in 2012, that year marking the 40th anniversary of the formation of the band.
In July 2016, the trio played a handful of UK shows beginning at Whitstable in Kent, with US and European dates following later in September and October.