Almost exactly 50 years ago Elmer Bernstein was unemployable; frozen out of Hollywood for allegedly un-American activities. Today, a month after his 80th birthday, he is being feted as one of the great movie composers, with over 150 soundtracks to his name, including an elite handful of iconic film scores – “The Magnificent Seven” and “The Great Escape,” to name but two.

This year he has already received the first World Soundtrack Lifetime Achievement Award from the Flanders Film Festival. Later this month he’ll receive another lifetime achievement award in Las Vegas. Last month, at a birthday screening in Newport Beach of “To Kill a Mockingbird,” for which Bernstein wrote one of his most important and influential scores, the city mayor declared April 14 Elmer Bernstein Day. Recently, Martin Scorsese, for whose film “Gangs of New York” (yet to be released) Bernstein has written the soundtrack, declared the composer “one of the great cinema composers of all time, whose breadth and amount of work shows a range that is quite unique”.

Last night the great wee man arrived in Glasgow to conduct the RSNO in an 80th birthday concert of his own music on Friday in the Glasgow Royal Concert Hall. Clearly, he’s on a roll. The man once eschewed concert performances of his own music, fed up with hearing it bastardised beyond recognition. (Just as well he doesn’t attend Parkhead where, whenever Henrik Larsson, number 7, scores, the crowd launches into the theme of “The Magnificent Seven.”) Yesterday Bernstein flew in from Barcelona, where he directed three concerts of his music on consecutive days last week.

He has been in Glasgow before. He was here in 1996, recording his beguiling, intimate score for “To Kill a Mockingbird” with the Royal Scottish National Orchestra. He was, he stated at the time, deeply impressed with the speed and quality of response of the RSNO; to the extent that he returned to make what he intended to be the definitive recordings of his scores to “The Magnificent Seven” and “The Great Escape” with the same musicians.

Famously, five years ago, he came to conduct the orchestra in a 75th birthday concert and to introduce at the Glasgow Film Theatre a screening of the audacious study of drug addiction, “The Man with the Golden Arm,” for which, in 1955, Bernstein produced the explosive jazz score that roared into the hit parade and started a trend among movie composers.

Now he’s back, and in his chosen programme on Friday will demonstrate just some of the extraordinary range of film music he has produced – from comedy and musicals to thrillers, actioners, and mood pieces; from “The Grifters” and “True Grit” to “The Age of Innocence” and the Oscar-winning “Thoroughly Modern Millie,” with, of course, all of his great signature pieces already mentioned.

His versatility has long since been his trademark; and his uncompromising honesty and integrity have won him the trust of generations of directors who know that, in the hands of the wrong composer, their films would be without colour, atmosphere, shape, or direction.

That versatility was evident from the moment his career was properly launched when, back to back in the mid-fifties, his epic score for Cecil B DeMille’s “The Ten Commandments” and his raunchy soundtrack to Otto Preminger’s “The Man with the Golden Arm” catapulted him into the top rank of composers for the big screen. Yet that launch nearly didn’t happen, and, immediately before it, Bernstein was more or less resigned to an existence in obscurity.

He had served his time. He’d done the training, begun a career as a concert pianist, and studied composition, encouraged by the profoundly innovative Aaron Copland, who, single-handed, forged a musical language with an authentic American accent that exerted a radical influence on US composers.

During the Second World War, Bernstein began writing music for radio drama. During this period he met novelist Millard Lampell who recommended Bernstein as composer for a football movie he’d written. The movie was called “Saturday’s Hero,” and young Bernstein had his foot in the door. Columbia hired him, and, in 1952, he wrote the music for the Joan Crawford thriller, “Sudden Fear.” Things seemed to be moving.

Suddenly, they dried up. “I fell victim to the political witchhunts of the time, and 1953 and 1954 became very lean years. Things were very difficult,” he recalls. He had been identified as someone working in the Hollywood establishment who had been associated with “un-American activities.” He was not a big name. He was at the outset of his career. There was no capital to be made out of pillioring him. Where bigger names were blacklisted, Bernstein found himself “greylisted”. The effect was the same: getting work became almost impossible. “I’d been involved in so-called left-wing activities. During the war we were allies with the Soviet Union and I’d done benefit concerts and such things for Friends of the Soviet Union. That was enough. It was a paranoid era and pretty terrifying.”

He occupied himself in tenth-rate schlock movies, and being the rehearsal pianist for ballet sequences in the film version of “Oklahoma!.” Then, in 1955, through a contact in Paramount, he was introduced to Cecil B DeMille. “Basically he rescued me by giving me the job to write the music for “The Ten Commandments.” Cecil was known to be very conservative, and, as far as the movie business and the establishment were concerned, they figured that if I was considered okay by an arch-conservative like DeMille, then I was not an immediate threat.”

Off roared his career. Clearly, he was a man for the epics. Equally, after “The Man with the Golden Arm,” he was the jazz composer – “I was never a jazzman,” he laughed. None the less, a spate of jazz-influenced scores followed, including “Sweet Smell of Success,” “The Rat Race,” and, unforgettably, “Walk on the Wild Side.”

Then came 1960, “The Magnificent Seven” exploded on to the big screen, and Elmer Bernstein was, overnight, the man for the westerns. Offers poured in, including seven John Wayne films and countless others. Bernstein still grins at the irony behind his great score for “The Magnificent Seven.” Everybody’s image of the movie is of a non-stop actioner.

“But when I looked at the film, when it was finally finished and before there was any music, it felt slow. Other than in obvious action sequences, it didn’t move on. I felt that the thing to do was to be like the jockey on a horse: go with the whip, and drive it along with energy; set up the audience right from the beginning and don’t give them a chance to look back. That’s why I wrote a deliberate Tex-Mex hell-raiser with a Latino feel.”

Sometimes he has worked by instinct, sometimes by protracted analysis with directors whom he trusts. “The Great Escape” is an example of the former, where the cheeky, jaunty, thumb-nosing, two-fingered little march, which has become a legendary whistling tune in its own right, was directly and instantly inspired by Steve McQueen’s indomitable Captain Hilts.

Bernstein’s lightly-textured soundtrack for “To Kill a Mockingbird,” a penetrating and evocative chamber music score that still exerts an influence today, was evolved through a long study of the film before a note was written.

On his career rolled, into the seventies where, through a contact with director John Landis, he wrote the score for National Lampoon’s “Animal House.” Overnight, and for almost a decade, he was the man for comedies, including “Airplane!,” “The Three Amigos,” and some of the music for “Ghostbusters.”

In sum, this charming, thoughtful, articulate, and accessible man is a consummate exponent of a craft he reveres and of which – in fear of its being squeezed out of existence by corporate attitudes – he is a fierce and persistent proselytiser. “It’s alarming how many pictures have become vehicles for promoting records, where a film is actually built around a pop song. I spend a lot of time now talking about the sins of the film-makers, but I must say that I shouldn’t exclude some of my colleagues, who do that sort of thing for venal reasons. They themselves are looking to use a film to exploit some song that’ll go to the charts and make a lot of money. I have to say that the art of film music is not flourishing in the greatest state of morality.”

Elmer Bernstein conducts the RSNO, Glasgow Royal Concert Hall, Friday, 7.30pm.