Imagine: Simon and Garfunkel - The Harmony Game, BBC One

“It’s very deep, very private and full of love,” said Art Garfunkel of his relationship with Paul Simon. So private that for this examination of their swansong 1970 album Bridge Over Troubled Water the pair were interviewed apart, despite both being credited as executive producers. Whatever the nature of the love, 40-plus years on, bridges weren’t being built.

Paul Simon didn’t seem too enthusiastic about revisiting his past. One of the few times a smile flashed across his face was when he recalled the journey he used to make to buy records by The Everly Brothers. Discussing the inspiration for the album’s deathless title track, he said he didn’t know where it came from. Yet a contemporary clip showed him with a guitar acknowledging the song's debt to gospel group The Swan Silvertones. As an executive producer, he must have been aware of the clip. Considering he repeatedly said he instantly knew “Bridge Over Troubled Water” was a monster song, the best he’d written, he must have memories of its genesis. And considering how many times he’s told the story of how “Homeward Bound” was composed, you were left suspecting that he was being contrary for the sake of it.

But that’s what you get with Simon and Garfunkel. There's a story that Garfunkel used to hitch-hike to the duo’s shows and that Simon and their manager Mort Lewis would pass him by in the car. It may be apocryphal, but in this documentary Lewis says, “Each day was better than the day before.” Depends who you are and what you mean by better.

Although the duo split in the wake of the album’s release and their relationship is a matter for themselves, understanding the dynamic between Simon and Garfunkel which led to creating their music is always going to be of interest. This careful, sanctioned documentary was more about the nuts and bolts of the album, its individual songs and their public life, including on the 1969 TV special Songs of America. Billed as part of the Imagine series, Simon and Garfunkel - The Harmony Game was a buy-in with a Sony Records credit as well as the one to Simon and Garfunkel. Such origins meant it wasn’t going to probe any further than those taking part would allow.

The sponsor of Songs of America pulled out, objecting to its 'humanist' stance

Even so, hearing their producer Roy Halee dissecting their sound was fascinating. The wordless chorus for “The Boxer” was recorded in a chapel at Columbia University. Session man Hal Blaine's booming drums on “The Boxer” were played in a corridor for maximum echo. Simon explained that the percussion on “Cecilia” came from a home-made tape that was sliced up and then turned into a loop which became the basis for the song. The other LA session men who played on the album stood up to account their roles.

The tension between traditional studio approaches and the ad hoc was mirrored by Simon and Garfunkel making political statements and sticking to their guns against the wishes of the suits. The sponsor of Songs of America pulled out after seeing the finished product, objecting to its “humanist” stance. An ice-skating special got higher ratings. Some statements were even a little too much for Garfunkel, who put a stop to Simon including his song “Cuba si, Nixon No” on the album.

Beyond the contradictions and tensions, here was a powerful reminder of what a terrific album Bridge Over Troubled Water is. Their version of The Everly’s “Bye Bye Love” isn’t its highlight, but hearing the title track afresh rammed home how breathtaking it can be. Especially with Art Garfunkel singing it at a microphone in a warehouse-like studio (see clip below). Lindsay Buckingham must have drawn on “Cecilia” for Tusk-era Fleetwood Mac. “The Only Living Boy in New York” made Fleet Foxes’ debt clear.

Directly or indirectly, the album will live on. Paul Simon and Art Garfunkel will do what they do. But there’s probably not going to be another officially sanctioned documentary on Bridge Over Troubled Water, so the failure to push this brittle pair to open up was a shame.

Simon and Garfunkel rehearse "Bridge over Troubled Water" in the 1969 TV special Songs of America