It's rare, if ever, to hear a kind word said about James T. Aubrey, the ruthless former CBS executive hired in 1969 to turn around the stuttering fortunes of the MGM movie studio.

In a four-year reign he slashed staff numbers, cancelled many projects and sold off the company's archive in a sale that, famously, included Judy Garland's iconic ruby slippers from The Wizard of Oz.

"They had no intrinsic value," was Aubrey's icy comment at the time.

And along with that brutal act, incredibly, he also ordered the destruction of many of the film scores in the company's archive, trashing music from legendary films including The Wizard of Oz, High Society and Singin' in the Rain.

These gems might have been lost forever were it not for the passion and dedication of English conductor John Wilson, who for the past 15 years has dedicated much of his time to re-creating them.

Now he has re-scored some 200 separate numbers from MGM musicals from the 1930s to the early '60s purely by ear, a task he was driven to largely out of necessity – he loves the music and wanted his orchestra, the John Wilson Orchestra, to play it.

"I had to do it," he says simply.

He's also quite frank about the tedium of minutely reconstructing each part.

"First and foremost, I'm a conductor – it's all I do really," he says. "I don't like writing music out but I have to. It's a pain in the arse! It's hours of toil.

"I do love hearing it back – I only do the numbers I think are really sensational – but sitting listening to four seconds of music on a loop for half an hour just to get one bass clarinet part ... is that going to be anything other than just necessary?"

One might then expect Wilson to join the chorus of Aubrey critics but he is surprisingly generous towards the man who presented him with a lifetime's work.

"It would be easy to say James Aubrey was a vandal but I think there were a lot of people around then who had no idea that this was worth keeping," he says.

The pace at which the studio system turned out films left little time for those involved to consider their longer term significance.

"If you had said to anyone in the 1930s that what they were creating was art they would have laughed at you," says Wilson. "It was entertainment designed to make a profit. Nobody was archively minded. A lot of the scores were an unfortunate casualty of that prevailing attitude. It would have been a case of, 'Who wants a load of old crumbly pages'?"

Wilson's passion for "good quality light music" sprang from the TV and radio when he was growing up in England's north-east in the 1970s.

After an extensive apprenticeship playing piano, arranging music and conducting for amateur dramatics, pantomimes and other productions he went on to study in London.

"By the time I arrived at the Royal College of Music at 18 I was fairly hands-on and practical," he says. "There were never any divisions for me between David Raksin, Max Steiner and Erich Korngold and Strauss, Mozart and Brahms."

Now he is working alongside his long-time friend and collaborator, Sydney Symphony Orchestra co-concertmaster Andrew Haveron, bringing his favourite light music to Sydney audiences.

Haveron has led the John Wilson Orchestra since its inception.

"Andrew knows how to play this music better than anyone on the planet. That's a real game changer," says Wilson.

On a program that also includes music from Citizen Kane, Gone With The Wind and Star Wars will be Erich Korngold's music for 1938's The Adventures of Robin Hood, starring Errol Flynn.

Wilson's face lights up. "It is," he says, "the greatest movie score that has ever been written. I never get past how impressive it is."

Hollywood Rhapsody is at the Sydney Opera House June 16-18.