John Battsek and Andrew Ruhemann didn’t set out to become the U.K.’s leading producers of theatrical documentaries.

But with an Oscar for their debut doc “One Day in September” in 1999, several acclaimed films since then and three more premiering at Sundance next month, they seem to have managed it anyway.

Surfing the rising tide of theatrical docs in recent years, their company Passion Pictures has become the first port of call for many established and aspiring docmakers with bigscreen ambitions.

This year alone they were behind two contrasting releases — Gary Tarn’s “Black Sun,” in which the testimony of a man blinded by robbers is married to mesmerizing, expressionistic images; and “Once in a Lifetime,” a brassy account of the rise and fall of the New York Cosmos soccer team.

At Sundance, Passion will unveil Dan Gordon’s “Crossing the Line,” about four American soldiers who defected to North Korea; David Sington’s “Apollo: In the Shadow of the Moon,” about the history of the U.S. space program; and Amir Bar-Lev’s “My Kid Could Paint That,” about a precocious 4-year-old artist.

They are now bidding to take their business to the next level by developing feature docs with Michael Davies, the Brit whose Gotham-based shingle Embassy Row brought shows such as “Who Wants to Be a Millionaire?” and “Wife Swap” to America. Davies already served as exec producer on “Once in a Lifetime.”

“Michael’s reputation in the U.S. will put us in a position to do stronger and more aggressive deals in rights ownership,” Battsek says.

What makes Passion’s eminence in the non-fiction field so unusual is that neither Battsek nor Ruhemann come from a conventional background in TV docs. In fact, Passion only started a TV arm three months ago.

Ruhemann founded Passion in the late 1980s as an animation producer specializing in commercials and pop promos. That’s still where the company, which animates the cartoon rock band Gorillaz, makes its money.

Battsek’s original dream was to play striker for the Chelsea football club, or failing that, to become Blighty’s best distributor, like big brother Daniel, who now runs Miramax in New York. Neither career path quite worked out.

Battsek spent five years producing his first dramatic feature “The Serpent’s Kiss,” but it sank without a trace. He joined Passion in 1997 to launch a film department, but “Serpent’s Kiss” had left him dispirited and disillusioned. It was only when he bought a ticket to see the Oscar-winning doc “When We Were Kings” that he found his true calling.

“Halfway through the movie, I realized that’s what I wanted to do,” Battsek recalls. This epiphany led to ‘One Day in September,’ and things have snowballed from there.

“There’s a sense of creative and personal satisfaction about dealing with the truth. For me, a documentary like Greg Barker’s ‘Ghosts of Rwanda’ is vastly more powerful than any of the dramatized Rwanda movies.”

Battsek did not produce ‘Ghosts of Rwanda,” but he is developing Barker’s next doc, “Killing the Flame,” about charismatic U.N. human rights commissioner Sergio Vieira de Mello, who went into Baghdad to help with the nation’s reconstruction after the fall of Saddam. De Mello and several colleagues were killed in a bombing that effectively ended the U.N.’s role in Iraq.

Passion is also seeking to balance its flourishing business of docs and commercials with a move into drama. It’s prepping a drama-doc version of “Unreasonable Behavior,” the memoirs of war photographer Don McCullin; and a dramatic feature based on Bernard Hare’s autobiographical book “Urban Grimshaw and the Shed Crew,” about a group of feral kids living wild in Leeds.

It’s even branching out into fiction, with an adaptation of Meg Rosoff’s apocalyptic teen novel “How I Live Now,” to be directed next year by Thomas Vinterberg.

“We are probably at the top of the pecking order for feature documentaries and a lot further down for drama,” Ruhemann says. “But we’re only one critical drama success away from where we want to be. Oh, and we’d love to find an animated movie to make.”