IF you require hard evidence of just how seriously Benny Gallagher and Graham Lyle take the art of songwriting, simply rewind to January 30, 1969.

On that date, the Scottish duo were so absorbed in composing a new song, they were oblivious to the fact that music history was being made just two floors above them.

The pair had been employed by The Beatles as house writers for Apple Records, at a rate of £25 a week.

In the label’s chaotic headquarters at No. 3 Savile Row in London, they were focused on putting the finishing touches to a track for Mary Hopkin.

But what they didn’t realise was that John Lennon, Paul McCartney, George Harrison and Ringo Starr were playing on the rooftop of the building in what would be their last ever live concert appearance.

After a performance of Get Back – the final song in a 42-minute set – Lennon quipped: “I’d like to say thank you on behalf of the group and ourselves … and I hope we passed the audition.”

The legendary gig will be seen for the first time in a new documentary directed by Peter Jackson to be premiered on the Disney+ channel later this month.

“I got a message recently from a guy in China who said, I was up on the roof for the whole concert,” revealed Benny. “I wrote back and told him, you were lucky, I had to work.

“Initially, George didn’t want to play live at all. They’d been trying to work out a way to do it.

“Brian Epstein, their manager, had died and that created chaos. Suddenly the whole organisation was rudderless. Paul said, well it’s only us now.

“It will be quite poignant to finally see the footage. But it was important for us to keep working. We were songwriters. It was our job.”

It proved an astute decision. When fashion model Twiggy saw Hopkin win the ITV talent show, Opportunity Knocks, she recommended the Welsh singer to McCartney.

He produced her 1968 debut single, Those Were The Days, which topped the UK charts for six weeks. It was only kept off the No. 1 position in America by Hey Jude by The Beatles.

“Paul sent a letter to all the writers saying he wanted the follow-up to come from in-house,” recalled Benny.

“He had a demo of a great song he’d written called Goodbye. We looked at each other and thought, that’s the single. He used our track Sparrow on the B-side.

“So the whole idea behind Apple was fantastic even if The Beatles didn’t quite carry it through in the end.”

When the label – whose artist roster included James Taylor, Badfinger, Doris Troy, Billy Preston and Jackie Lomax – fragmented, the Scots musicians struck out on their own. In 1970, they were founder members of McGuinness Flint, writing nine of the 11 songs on their debut album including hit singles, When I’m Dead And Gone and Malt And Barley Blues.

“It came at a perfect time for us. Apple had started to fall apart,” said Benny.

“A friend knew the band was looking for a bass player. He said, I know these two guys but they’re a team, they come together.

“At the first rehearsal we came up with the idea for When I’m Dead And Gone. Later, I phoned Graham and said, I think I’ve got a title for this. There was a silence, and he replied that’s a bloody cheery name for a song.”

It was while working on the track that Graham was thrust into the spotlight.

“We recorded it with singer Dennis Coulson but it didn’t really suit his voice,” he said. “So they asked me to sing it, but I wasn’t used to being up front. I was perfectly happy writing songs and staying in the background. But when they put me on the mic I was amazed. It brought images of Buddy Holly, Richie Valens and people who had influenced me into my head. I knew it was going to be successful.”

After recording a second album the pair moved on to form Gallagher and Lyle two years later. Their self-titled debut was released on EMI-Capitol before they signed to A & M Records and made Willie And The Lapdog (1973), Seeds (1973) and The Last Cowboy (1974).

The foundations of the career-defining Breakaway, came as the semi-acoustic duo were developing a more full-band sound. It proved a bold step and there was a lot at stake.

“It was make-or-break time for us. Our houses were on the line. Real backs to the wall stuff,” admitted Benny.

“We’d done a tour with an orchestra but the record company had not really promoted it. We thought, we’ve got to write our way out of this problem. So we came up with about 30 new songs. When we started on Breakaway we had no idea if we’d achieved that or not. We were both so lost in working on it.”

The album was recorded at AIR Studios in London with US producer David Kershenbaum and engineer Geoff Emerick, who’d worked on The Beatles’ albums, Revolver, Sgt. Pepper’s Lonely Hearts Club Band and Abbey Road.

“Geoff was an amazing character. I remember saying to him, that’s the best vocal sound we’ve ever had,” recalled Benny. And he blushed. A guy who’d worked on so many big records was actually embarrassed at me saying that.”

While A & M kept their distance, the heat was on for the duo to make a major breakthrough.

“They were very supportive and stuck with us through each album before we even got to Breakaway,” recalled Graham. “Today, a new artist would probably be lucky to get one record to see if they were going to be a success. But they backed us all the way. You only had to look at acts like Supertramp, Joan Armatrading and Chris de Burgh to see that. All of them are still out there writing and playing.

“A & M depended on that quality and it paid off for us.”

As the album took shape, the duo realised they’d recorded some of the finest songs of their career.

“We worked our bums off non-stop to try and make a great record,” said Benny.

“Geoff was an expert in setting up stuff and catching it as it goes. There seemed to be far too many long days and nights, but we got there eventually. Without him and David we’d have been on our knees.”

Breakaway was released in February, 1976, and three songs stood out as potential singles … Heart On My Sleeve, I Wanna Stay With You and the title track.

“I thought we needed a real radio single to get us out of the mire,” said Benny. I felt I Wanna Stay was our best shot, while Graham preferred Heart.

“We played both to the head of the label. After he heard Heart he said, I think you could get a cover from Alvin Stardust on that. We immediately slumped. But in the general scheme of things good sense prevailed.”

Both songs were Top 10 UK hits, and Breakway peaked at No. 35. The album reached No. 6. DJ Dave Lee Travis introduced their appearance with Heart On My Sleeve on Top Of The Pops on June 17.

“We’d been on tour in America with Supertramp and Chris de Burgh and flew back to London. We didn’t even go home, we went straight to the BBC,” said Benny. “Nils Lofgren, who is now a member of Bruce Springsteen’s E Street Band, had come to see us play in Washington. He asked if he could play accordion with us on the show. But his flight got held up and he didn’t make it.”

Now, 45 years on, the duo regard Breakway as their finest musical moment. “It’s some of the very best work we have ever done,” said Benny.

“And that’s not to take away from any of the previous acoustic albums because there are some wee gems of songs on them too. I’ve not listened to Breakaway in full for a long time. I don’t even have a copy of it at home.

“But I’d be quite happy to walk into any room and play those songs to an audience. It’s a great record. We were just learning our trade really.”

THE Billy Sloan Show is on BBC Radio Scotland every Saturday at 10pm.