When Giles Martin was asked to work alongside his father and remix the Beatles for Love, a Cirque du Soleil show based on the band’s back catalogue, he wasn’t sure he should take it on. “If anyone told me they were going to get George Martin’s son to mix the Beatles and put on a show in Las Vegas, I’d probably have punched them,” he says in his well educated voice, as he puts down his mint tea. “Because it’s a repulsive idea.”

He resisted not only because of the inevitable accusations of nepotism but also because he wasn’t sure it would be successful. But he was wrong. Since Love opened in a $100 million theatre in Vegas in 2006 — with a staggering 7,000 speakers and enough dancers, mime artists, trampolinists and bungee jumpers to keep any Cirque fan content — it has virtually sold out every night.

It was the first time that Apple, the protective Beatles organisation, had licensed songs for a theatrical production, bowing to the friendship between the late George Harrison and Guy Laliberté, the founder of Cirque. Which meant that it was the closest thing to a Beatles gig, albeit a very modern one. Perhaps most importantly, Love has the blessing of Paul McCartney, Ringo Starr, Yoko Ono and Olivia Harrison.

And now, for those who couldn’t make it to Vegas (where there will be two shows a night for the next eight years), there’s a new documentary about the making of the show. All Together Now, directed by Adrian Wills, avoids sentimentality to provide a fascinating, fly-on-the-wall insight into what was clearly a mammoth task. One scene shows George Martin, whose hearing is failing but whose musical sensibility has yet to fade, conducting the orchestra, perhaps for the last time. As they play a fragile version of My Guitar Gently Weeps, Giles respectfully looks on.

It is technology that separates father and son in the studio. “My dad is 82,” says the 38-year-old Giles. “He’s got a Mac — he’s pretty good, but it’s not his world. I had to explain the mash-up mentality of grabbing one piece of music and sticking it with another, even though he’d done it subconsciously in 1967 on All You Need is Love by using Greensleeves and In the Mood in the orchestral fade-out.”

All Together Now has its unexpected moments too. At the premiere of Love, McCartney turns to Starr and says, almost surprised: “What a great f***ing band we were.” Sitting in his plush Vegas seat, Sir Paul then sings along to Sgt Pepper’s Lonely Hearts Club Band with joyous abandon. Yet, for the two widows, it seems to have been a more poignant experience. Olivia Harrison concludes sadly that Love was “physically unsatisfying but spiritually satisfying”, while Yoko Ono hides behind her sunglasses and says, “I feel sad that he [Lennon] is just a voice now.”

I ask Giles if Ono’s omnipresence at the Love rehearsals was a help or a hindrance. He smiles. “Yoko is incredibly straightforward. Not in a bad way, funnily enough. She wrote a huge précis of what she didn’t like and the director, to his credit, agreed. She’s very sweet and kind. When my daughter was born a year ago the first gift was a beautiful engraved silver cup from Yoko.”

When asked who proved the most challenging to work with, Giles immediately names McCartney. “He remembers everything and he’s way more musical than me. I couldn’t get away with anything. But I’ve always had a good relationship with Paul. He picked me up in his car once when I was young and asked me about music. I told him it was difficult to write songs. He said: ‘Well, I’m Paul McCartney and I find it hard to write songs. Don’t you give up now.’ He got his assistant to send me a guitar.” He whispers then laughs. “It was crap, looking back at it.”

The young Giles always wanted to meet John Lennon but Lennon was killed when he had just turned 11. “I wish . . . it’s a strange thing . . .” For the first time in the interview he loses his veneer of confidence. He seems close to tears. Then he pulls it together. “Funnily enough, I’ve got the same birthday as him. When I was born he said to my dad: ‘Now you know what sort of a***hole he’s going to turn out to be.’ Which is very John Lennon.”

The day Lennon was shot is burnt into Giles’s brain. “My parents were watching the news on TV. They were absolutely shocked. It was chaos in our house. My dad was working with Paul at the time, I think. In that two-week period Peter Sellers also died. My dad had worked on comedy records with him and he was a really good friend.”

What next for Giles Martin? “There’s a Brian Wilson project I’ve been asked to do,” he says. “I think God Only Knows is one of the best songs ever written, so I’m keen on that. At the moment I’m working on a Martin Scorsese music documentary. I’ve learnt almost everything I know from my dad, so I feel incredibly lucky.” He smiles. “Not that we sit around talking about the Beatles all the time. Mostly we just watch the snooker together.”

All Together Now will have its premiere at the Raindance Film Festival, London, on October 9 at 9.15pm (raindance.co.uk/site)

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