The argument about possessory credits and the creative heft of the screenwriter is almost as old as the film industry itself.

It predates the squabble between Herman Mankiewicz and Orson Welles over the writing credit on Citizen Kane - which the director wanted all for himself; it underpinned the on-set shouting matches between Frances Marion (the highest paid writer of the 1920s) and MGM honcho Irving Thalberg; it was already bubbling under in the 1910s, when writers' contracts first featured the insidious clause "the studio, hereinafter referred to as the author".

Ronald Harwood, the 'author' of The Diving Bell And The Butterfly, took up the good fight again at the recent Cheltenham Screenwriters' Festival, stating, with some justification, that "directors have an inclination to sweep away the writer, and the media buy into it".

Knockout script

I watched On The Waterfront again the other evening. I had not seen it for more than 20 years, and my memory of the film centred on Marlon Brando's performance. This time round, it was Budd Schulberg's script that stood out.

In particular, I was floored by the economy of the opening. Within the first four minutes we have everything we need to carry us through the film. The setting - Hoboken docks, New Jersey - is not only presented visually but characterised as a place of poverty and corruption, where a cowed workforce is kept in place by mobster-like union bosses who are willing to murder to ensure obedience.

The inciting incident kicks in with textbook precision (even a tad earlier than usual) at the end of the second minute, when canary Joey Doyle - a docker who is about to testify against the bosses - is pushed off the roof of his tenement block.

The cynicism of the cull worms its way into the conscience of Terry Malloy (Brando), the none-too-bright former boxer who was sent by union boss Johnny Friendly to lure Doyle to the roof. Doyle's sister Edie, who hunches, grieving, over the body, is all righteous fury (her black and white view of life and morality will later almost derail her love story with Terry) while Father Barry, the hard-boiled West Side priest who tries to soothe her with the mantra "time and faith" is a man who is clearly heading for his own crisis of conscience as he realises this community needs more than religious quietism.

But when I tracked down Schulberg's shooting script, I realised just how much director Elia Kazan, director of photography Boris Kaufman and editor Gene Milford had contributed to the brilliance of the stunning introduction.

Schulberg's script has Terry walking alone from the union hut to lure Doyle with the bait of a stray homing pigeon; in the film he is boxed in by Friendly and three other union mobsters. In long-shot, he looks like a condemned man being led to the electric chair.

For Schulberg, the victim Doyle is "a youthful, rather sensitive and clean-cut Irish boy"; for the audience, he is a backlit ghost - a premonition of his rooftop effacement. In Schulberg's script we go on the roof with Joey; in the film a view of two ominous thugs standing up there like angels of death, followed a little later by the flight of the body, is all we need. Was this punchy economy Kazan or Milford's idea'

Most striking of all, perhaps, is the fact Terry's walk towards his betrayal of Doyle starts in the light of day and ends in creepy, shadow-laden darkness - whereas Schulberg has 'Night' on all his scene headings.

Harwood is right to insist on greater creative recognition of the screenwriter as co-author of the cinematic artefact. But authorship in film is a tricky business. Maybe Mike Leigh - another of this year's Cheltenham speakers - is right to say the only real solution to the dilemma is to be a writer-director. That way, "I don't have some bastard hack telling me I can't touch his sacrosanct lines, and I don't have some bastard director touching my sacrosanct lines."

But hold on - Leigh famously works his scripts in improvisation workshops with his actors. Doesn't that make them authors too'