It's a piece of sweet synchronicity worthy of Hollywood itself. This year marks the 70th edition of the Edinburgh International Film Festival and 70th birthday of legendary filmmaker Steven Spielberg, whose planet-conquering classic ET the Extra Terrestrial had its UK premiere at the EIFF in 1982.

How better to celebrate this triple anniversary than with the first British screening of the film accompanied by a live orchestra performing John Williams' immortal score?

'A lot of people haven't seen ET on the big screen for a long time,' says EIFF Artistic Director Mark Adams, 'and I think that music played by a full orchestra in the Festival Theatre gives it a real sense of atmosphere and occasion. It's a proper film event.'

The event marks the second time that the Royal Scottish National Orchestra have collaborated with the EIFF in as many years, following last year's sold-out screening of Back to the Future with a live orchestra. Dutch conductor Ernst van Tiel, who will lead the RSNO during this year's performance of ET, agrees: 'You cannot compare the concert with live orchestra and going to a cinema. It's something totally different, the impact is huge.'

No stranger to the world of cinema, van Tiel conducted Ludovic Bource's celebrated score for the multi-award-winning French sleeper hit, The Artist. He's also travelled the world conducting orchestras at special screenings of classics such as Sergei Eisenstein's Alexander Nevsky (1938) and Fritz Lang's Metropolis (1927), and has mounted the podium for celebrations of great screen composers such as Hitchcock collaborator Bernard Herrmann.

Yet despite his admiration for Williams' work, van Tiel has a confession to make: prior to signing up for this performance, he'd never actually seen ET before. 'But when I started to study I saw the film and heard the music, and it was so affecting and so well done. A computer can write music like Mozart, but the only thing missing is that something that you cannot describe. That's what a good score is, and I think ET is maybe John Williams' best.'

It's certainly one of the most well-known and beloved scores in cinema history. You could, of course, say the same of so many Williams scores, from those he wrote for the Superman and Star Wars sagas, to his many collaborations with Spielberg including Close Encounters of the Third Kind, Raiders of the Lost Ark and Jaws.

'He seems to have found that magical link with two or three filmmakers,' says Adams, 'where they create a sense of majesty and adventure and a spiralling sense of occasion. You look at Star Wars and Raiders, [and] his work is so distinctive; you feel a building sense of excitement when the music kicks in.'

For RSNO chief executive Krishna Thiagarajan, Williams is 'one of the most influential composers of our time.' He also believes that concerts of this kind draw an important link to the origins of cinema itself. 'It's only when the movies learned how to talk that the music disappeared from movie theatres,' he says, 'but most of the theatres that were built early last century had entire orchestra pits installed as well. So in a way we're doing something that seems modern, but actually 100 years ago was completely normal.'

Recalling the early days of live cinema accompaniment, van Tiel waxes lyrical about the art of the sound maker, or gerauschemacher in German: 'He would make sound effects, ringing bells, firing gunshots, all those things were done by him. Also there was a time when the big cinema organs had everything, they had piano sounds, trumpets, military drums played by very high level musicians.'

Van Tiel believes passionately in the importance of film composition, not only as an art form in its own right, but also as a gateway into symphonic music for modern audiences. He recalls, 'When I was conducting in a university in Holland, for Adagio for Strings by Barber, almost all the students were suddenly totally quiet and said, "We know this!" They liked it because it had some context with the film Platoon. Another example is Walt Disney's Fantasia, which for many people was their introduction to The Sorcerer's Apprentice and Bach.'

He also believes that, were they alive today, many of the great classical composers, Stravinsky and Wagner in particular, would be working in cinema. Film composition, he argues, is no longer seen as a lesser art form.

'In the past, on the high level, there was opera and ballet. They were at the top, and film music was much less appreciated. But in the last few years it's almost on the same level, and I'm very happy with that because for me film music, opera and ballet are all theatre music. There is lots of good film music and I love to conduct it, because what happens in the hall with the film and the orchestra, it's like exploding a bomb. The feeling that we are creating something new at that moment gives such an extra impact to everybody.'

EIFF and RSNO present the UK premiere of ET the Extra Terrestrial with a live orchestral score on Sat 25 Jun, Festival Theatre, Edinburgh.

Tickets on sale now.