David Lean's Brief Encounter may seem very innocent now, but it was banned in Ireland on its first release, writes Donald Clarke.

Heads up, swivel-eyed social conservatives. Prepare your placards. Begin rehearsing your rosaries. Yet another piece of cinematic filth, once banned in this country, is set to ooze its way onto the screens of the Irish Film Institute.

Is it Natural Born Killers? Could it be I Spit on Your Grave? No, the outrage in question is that timeless celebration of romantic denial, Brief Encounter. Hard though it may be to believe, David Lean's clipped drama, which is revived in a beautiful new print this week, was indeed deemed too shocking for the nation's cinema-goers on its release in 1945.

The Irish censor, conscious that the picture detailed an adulterous romance, somehow managed to locate "numerous seductive and indelicate situations" amid the grey tea and moral anguish. It was another 17 years before Brief Encounter - some indelicacies filleted - made it into Irish cinemas.

So, what did the censor see that so many others have missed? Brief Encounter, an expansion of Noel Coward's theatrical vignette, Still Life, follows the relationship that develops after a frustrated housewife allows a handsome doctor to pluck a piece of grit from her eye at a suburban railway station.

Told in flashback as Laura, played by a crisp, frail Celia Johnson, journeys home to her dreary husband following one last encounter with Trevor Howard's more worldly Alec, the film comprises hurried clinches in tunnels, innocent trips to the pictures and endless debates as to just how impossible their situation is.

"I want to die. If only I could die," Laura says in one typically uproarious moment. The film would form a pleasing double-bill with Brokeback Mountain in any season focusing on the beautiful misery of frustrated love.

The main controversies attaching themselves to Brief Encounter in recent years have involved punch-ups between British critics over the quality of the picture. When Derek Malcolm, the Guardian's veteran film writer, published a list of 100 great films of the last century, he left out Lean's Lawrence of Arabia, but found space for this quieter, more nuanced work.

"Brief Encounter remains a piece of cinema remembered with affection by almost everybody who saw it," Malcolm wrote. Well, yes, almost everybody.

Geoff Andrew, a film critic for the perennially right-on Time Out magazine, is, it appears, one of the exceptions. "I detest Brief Encounter," he said when asked about Malcolm's list.

Elsewhere, Andrew has explained that he feels all that "stiff-necked restraint" mars the piece and helps demonstrate exactly "what is wrong with so much of British cinema". Really? It seems unlikely that he would write those words about similarly emotionally curbed films from Japan or China. Surely restraint - as much as violence or comedy - is one of the key cinematic colours at any director's disposal.

More worrying now is the film's attitude to class. Whereas the romance between Alec and Laura is seen as unimaginably tragic, that between Stanley Holloway's bluff station-master and Joyce Carey's prim cafeteria manageress is played for laughs. One senses that Coward felt the lower orders incapable of experiencing the complex emotions suffered by tweedy doctors and ladies with handbags.

Mind you, none of this would have been likely to worry the Irish censor. Maybe he was privy to the same insights enjoyed by some French critics. In the film's tensest scene, Alec and Laura, scandalously alone in a bachelor flat, appear to be on the point of doing something unspeakably carnal, when the apartment's owner, a colleague of Alec's, bursts in on them. Lean was astonished to discover that in France many viewers assumed that the two men were lovers.

While acknowledging the Gallic tendency to identify everything English as gay, one can still see why this was a conclusion worth jumping to. Alec's mate, played with overpowering loucheness by the inimitable Valentine Dyall, does seem inordinately appalled by the tryst he has interrupted. "This is a service flat," he sneers. "It caters for all tastes." Dyall's tone suggests he has just caught Alec with a sheep and a rubber glove.

Perhaps we read too much into this scene. But Coward, a gay man in an era where homosexual acts were still illegal, must surely have sympathised with Alec and Laura as they are forced into lies and furtive evasion to cover up their relationship.

This most chaste of films does still work as a powerful allegory for the British gay experience in the years before the legal reforms of the 1960s.

But is it possible to take the film literally? Surely, even in 1945, Alec and Laura would have hopped into bed together. "They might well have screwed like rabbits in real life," David Lean said, "But this was real life as J Arthur Rank insisted on us seeing it." Brief Encounter may have been clean enough for Rank, the great British studio chief, but not, it seems, for the good people of Erin.

• Brief Encounter opens at the Irish Film Institute tomorrow.