Directed by John Schlesinger, it stars Tom Courtenay (who had understudied Albert Finney in the West End theatre adaptation of the novel) as Billy and Julie Christie as Liz, one of his three girlfriends.

To escape the boredom of his humdrum existence, he constantly daydreams and fantasizes, often picturing himself as the ruler and military hero of an imaginary country called Ambrosia.

Billy has further complicated his life by proposing to two very different girls, the sheltered, virginal Barbara and the tough, brassy Rita.

She urges him to accompany her to London that evening, and he goes home to pack his bags, only to find his grandmother has fallen ill and been taken to hospital.

He then continues to the station to meet Liz, and the couple board the train, but at the last minute Billy disembarks with the excuse of buying some milk to drink on the journey.

He delays returning to the train, and by the time he gets back it is pulling out, with an understanding Liz at the window and his suitcase left behind on the platform.

Alone, Billy walks the dark deserted road back to his home, imagining himself leading the marching army of Ambrosia.

But the most memorable moment remains the sight of Julie Christie on the train to London, watching Courtenay shrugging on the platform and settling for the mediocrity he despises and probably deserves.

While director John Schlesinger was solidly Hampstead, Waterhouse was a dropout from Osmondthorpe Council School, Leeds, and star Tom Courtenay the son of a Hull dockworker.

As the box office boomed, a daydreamer might have conjured up a British film industry filled with working-class actors and writers, maybe even directors and producers, too.

"[11] In 2020, Slant magazine considered Billy Liar heir to the innovative cinematography developed by Truffaut and its main character somewhat a precursor to A Clockwork Orange's Alex DeLarge.