Bollywood is the world’s most prolific film industry, but for decades one plotline has dared not speak its name. Now the sub-continent’s ultimate cinematic taboo is to be broached, with the first depiction of a gay kiss.

Months before its release, Dunno Y . . . Na Jaane Kyun has already been called India’s answer to Brokeback Mountain. The film, which promises to break new ground by telling the story of a serious, and explicitly sexual, relationship between two Indian men, comes months after a law outlawing homosexuality was overturned in the Delhi High Court.

It will star Kapil Sharma, an actor in his debut role who plays an aspiring gay model forced to “compromise his morals” to further his career. Its director, Anil Sharma, is one of the best known in Bollywood whose most recent offering, Veer, was a macho action adventure.

Little more is known of the project, which is due to premiere in May, but promotional posters showing two semi-naked young men in a passionate embrace have already fuelled controversy.

Gay activists say that they are braced for a backlash from religious and political conservatives, many of whom opposed the repeal of Section 377 of the Indian Penal Code — a law first framed under British rule that bracketed homosexuality with bestiality and paedophilia as crimes “against nature”, punishable by up to ten years in prison.

The decriminalisation of homosexuality is awaiting final approval by the Supreme Court, which is expected to be given after the Government backed the move last year.

For his part, Sharma insists that Indian cinemagoers are “mature enough” to deal with a story line that departs from Bollywood’s staple boy-meets-girl romances and bombastic action films.

“The only thing I was particular about was that this character should not come across as a caricature or just as an object of mockery,” the actor told The Times of India.

Meanwhile, gay rights campaigners say that they will reserve judgment until they see the film. “Just having two gay men on screen doesn’t mean they will depict a gay relationship,” said Gautam Bhan, a leading activist.

“It would be disappointing to discover that the hero ‘compromises his morals’ by getting involved with a man.”

In merely depicting a gay embrace, the Dunno Y promises to break long-held taboos.

Heirs to the creators of the Karma Sutra, the film-makers of India have often displayed a surprising coyness. Until recently, even heterosexual kissing — or “lip-lock” in the parlance of Indian newspapers — was regarded as somewhat edgy.

Recent films have nudged boundaries — albeit sometimes in questionable directions. New York, a film based around the 9/11 terror attacks, made headlines after it showed the buttocks of the leading man, John Abraham.. Dostana, a hit last year, portrayed two straight men who pretend to be gay to persuade a beautiful girl to become their housemate.

Leading gay figures now hope that Bollywood can play a part in changing attitudes — even where the treatment is satirical.

Ashok Row Kavi, the founding editor of the Bombay Dost, India’s only gay magazine, said: “Sure, Dostana was about a couple of fake gays but there’s a scene where a mother accepts her son’s homosexuality, and for a mainstream Bollywood movie, that was a very big deal.”

It started with a kiss. . .

The film Wings (1927) is credited with the first ever on-screen kiss between two men. The handsome young soldier Jack, played by Charles "Buddy" Rogers, places a lingering kiss on the lips of his dying friend, played by Richard Arlen

Just three years later, the first lesbian kiss featured in the film Morocco (1930). In her screen debut, dressed in a men's tuxedo and top hat, Marlene Dietrich played a cabaret performer who kissed a young lady in her audience

Sidney Poitier and Katherine Hepburn starred in Guess Who's Coming To Dinner (1967), which dealt with the then-taboo subject of interracial marriage, which was still illegal in 17 US states. Poitier plays an angelic young doctor who has a whirlwind romance with Hepburn, to the dismay of her parents

With Never Say Goodbye (2006), Bollywood finally broke the taboo surrounding the adulterous wife. In the blockbuster film, Shalini, a magazine editor, leaves her journalist husband after falling in love with an accountant