Meet the secret winner of The X Factor

Music producer and songwriter Steve Mac is almost as vital a part of Simon Cowell's empire as Cowell himself.

The winner of Britain's biggest singing contest will be announced tonight in front of an estimated 20 million viewers, and the resulting single from Rebecca Ferguson, Matt Cardle or boyband One Direction will become, instantly, one of the biggest-selling songs of the year. And Cher Lloyd, who was voted out last night, is also likely to get the chance of a hit.

Once again Simon Cowell will dominate proceedings – regardless of who wins – as the controlling mind behind Syco, one of the most impressive music machines in the world. But for all his influence, the winning acts from The X Factor, Britain's Got Talent and indeed the whole Cowell juggernaut would be deeply diminished if it were ever to lose the services of the power behind Cowell's throne: music producer Steve Mac.

Working from his own studio, Rokstone, in London, Mac is arguably Mr X Factor; the force that forged the huge catalogue of hit recordings by winners and runners-up, including the biggest stars to emerge from the show: Leona Lewis and JLS.

Co-writer of JLS's first No 1, "Beat Again", the Mobo and Brit award winner has more than 20 No 1 singles under his belt. His imprimatur as a songwriter and producer is also on Britain's Got Talent runner-up Susan Boyle, Pop Idol Gareth Gates and Louis Walsh's band Westlife as well as recordings by previous X Factor alumni Leon Jackson, Steve Brookstein and Rhydian Roberts.

Like Cowell, Mac – his full surname is McCutcheon – is a controversial figure in the music business. He now works almost exclusively for Cowell's artists, which some observers say has isolated him from the rest of the industry.

"He's made a pile of money, so he probably doesn't need to work for anybody else," one said. "Good for him and good luck, he's worked hard. But people no longer try to get him."

The broadcaster and music historian Paul Gambaccini added that Mac was one of the most successful producers of recent years. "He is representative of his era," he added. "His skill is the same as that which makes The Sun newspaper the most popular in the country. It has the knack of writing the headlines and identifying a story with the understanding of popular appeal. It is very unlikely that the reality show records are going to be fondly remembered by audiences in 30 years."

Mac began learning the piano aged eight and, despite expressing a desire to be an architect, followed family connections into the music business while doing work experience at his father's recording studio.

A spokeswoman for Cowell said it was too early to say who would be involved with the winner of this year's X Factor. "It all depends on the artist and the songs," she said.

Studio whizz: Steve Mac's hits for TV talent show alumni

2002: "Unchained Melody"

Gareth Gates, Pop Idol runner-up

Sales: 1.4 million copies

2002: "A Moment Like This"

Kelly Clarkson, American Idol winner

Sales: one million plus

2004: Il Divo

Debut album by Il Divo, the multinational operatic quartet created and managed by Simon Cowell

Sales: four million plus

2005: Heart and Soul

Debut album by Steve Brookstein, winner of the first series of The X Factor

Sales: 250,000

2006: "A Moment Like This"

Debut single by Leona Lewis, winner of series three of The X Factor

Sales: downloaded 50,000 times within 30 minutes of its release

2007: Spirit

Leona Lewis's first album

Sales: 6.5 million copies

2007: One Chance

Debut album by Paul Potts, winner of the first series of Britain's Got Talent

Sales: 3.5 million copies

2009: "Beat Again" (co-written by Steve Mac)

Debut single by JLS, runners-up of series five of The X Factor

Sales: in excess of 100,000 copies; it also won best single at the Mobo and Brit awards

2010: "The Club Is Alive" (co-written by Steve Mac)

First single from JLS's second album

Sales: 84,000 copies in a week

2010: The Gift

Second album by Susan Boyle, runner-up on the third series of Britain's Got Talent

Sales: 1.5 million copies to date