A little more on the part played by Isla Cameron.

From Mainly Norfolk; Thank you, Reinhard;

Isla Cameron sang Bushes and Briars in 1966 on her self-titled Transatlantic album Isla Cameron. She also was involved with this song in the 1967 film Far From the Madding Crowd. The liner notes of Sony’s 1991 soundtrack CD commented:

"For Far From the Madding Crowd, both [music composer Richard Rodney] Bennett and [director James] Schlesinger chose as their folk music advisor Isla Cameron, a mutual friend of both of them and a major figure in England’s postwar folk song revival. “Isla knew the music from Dorset and Somerset, having grown up there,” Bennett recalled. “Certainly she knew it better than I did—I knew very little about folk music or Dorset, and wasn’t that familiar with Hardy at the time.”

"Cameron selected the songs and musicians that would actually appear on screen (including virtuoso fiddler Dave Swarbrick, whose work can be heard behind Terence Stamp on his version of Tinker’s Song) and trained Julie Christie to sing Ralph Vaughan Williams’ Through Bushes and Through Briars. Cameron also sang the version of Through Bushes and Through Briars heard as background music later in the film, and appeared in a scene that was dropped from the final print, playing the directress of the seamstress shop where the doomed Fanny (Prunella Ransome) takes a job."

Strange enough, MGM’s original soundtrack album of 1867 contains the version of Bushes and Briars sung by Isla Cameron (and Tinker’s Song and I Sowed the Seeds of Love sung by Trevor Lucas). Sony’s 1991 soundtrack album restored the versions of these three songs sung by the actors Julie Murphie (Christie!), Terence Stamp and Paul Dawkins, and moved Isla Cameron’s and Trevor Lucas’ versions as bonus tracks to the end of the CD. Isla Cameron’s and Trevor Lucas’ recordings were also included in 1987 on the BBC album Through Bushes and Briar.

And from Wikipedia;

Isla Cameron was born in Blairgowrie, Scotland, but spent her childhood and teens in Newcastle upon Tyne. She acted in the 1967 version of Far From the Madding Crowd but her contribution was left on the cutting room floor. However, her voice appeared on the soundtrack album, singing "Bushes and Briars" (Julie Christie mimed in the film) and "The Bold Grenadier". Trevor Lucas, later to become the husband of Sandy Denny also sang on the album, and Dave Swarbrick played on some of the tunes. Her most prominent acting role was as the stern librarian Miss McKenzie in the 1969 version of The Prime of Miss Jean Brodie, where she could use her Scottish accent to advantage.

A footnote;

Wikipedia notes; "In 1959, Cameron appeared, uncredited, in the film Room at the Top." A film in which Andy Irvine also played a part!
[Raymond]        IRVINE, Andrew
[thespians member]        CAMERON, Isla