As the cost of making and promoting movies continues to spiral, it seems as if we are now living in an age when filmmakers are delighted just to break even, let alone make a profit.

Occasionally, a modestly budgeted sleeper hit will capture the public imagination (The Full Monty, Billy Elliot, My Big Fat Greek Wedding).

But these are few and far between.

Back in the heady days of 1972, one adult film became a cause celebre for an entire nation and made buying a ticket into an act of revolution.

Made for a paltry 25,000 US dollars (£13,700), Deep Throat was released at the very moment that America's mood swung towards sexual liberation and equal rights.

Religious leaders and political figures were understandably disgusted by this sudden acceptance of depravity and demanded action.

The ensuing furore over the film's explicit content persuaded President Nixon and his administration to declare war on smut.

At one point, Deep Throat was banned in 23 states.

But the controversy only served to increase public appetite for the film.

Today, Deep Throat is regarded as one of the most successful films of all time, grossing in excess of 600 million US dollars (£329m) worldwide.

This is a fascinating and absorbing, if rather lightweight behind-the-scenes account of the adult movie industry.

Unfortunately, the key player, Lovelace, only appears in archive footage, having famously denounced the film.

Inside Deep Throat includes snippets of the porn classic (justifying the 18 certificate), which proves it was the right film in the right place at the right time.

INSIDE DEEP THROAT (18, 89mins) Documentary. Narrated by Dennis Hopper. Released June 17.