He started out as a classical musician, switched to being a jazz saxophonist, joined the prog rock band Soft Machine and made his name as a composer in the world of advertising (remember that Cheltenham And Gloucester ad with the boy diving for a pearl?).

Then in 1995, he started writing for the concert hall.

It's no wonder Karl Jenkins tries to "resist putting music into categories".

When pushed, however, the Welsh composer will say that he writes "accessible music within the parameters of classical music", a fact which recently led to him becoming the only living composer in the top ten of Classic FM's Hall Of Fame.

Having established his popularity with Adiemus (a quasi-tribal choir project he compares to "jazz skat singing") and The Armed Man (which incorporated texts from the Mahabharata as well as standard mass movements), in March Jenkins once again hit the top of the classical charts with a piece set around both the traditional Latin mass and Japanese haiku poetry and dedicated to his father.

Now the UK's biggest-selling living composer is taking Requiem on tour and he hopes the Sussex premiere will draw a new audience for live classical music.

"In days gone by Mozart or Bach or whoever wrote pieces for an occasion, whether the Church or the Court," he says. "A lot of classical composers have lost that engagement with their audience. I have a different sort of occasion because I have a record deal with EMI Classics so I have to periodically come up with an album. That's my sponsorship - not God or a duke but EMI Classics."

Although wry and self-deprecating, Jenkins, who sees no shame in comparing himself to Catherine Jenkins and Andrea Bochelli, has no doubts about the worth of "chart-topping" music.

"There are," he observes, "two strands of classical music. There's the popular classical side to which I belong, and there's the more difficult side where new pieces often get one performance and nobody hears of them again."

Tomorrow Jenkins will himself conduct the opening night of the Requiem tour at Guildford Cathedral but on Sunday the baton will be passed to John Gibbons, a former Lancing College student who is also Principal Conductor of Worthing Symphony Orchestra.

He will be joined by the Apollo Voices and the West Kazakhstan Philharmonic Orchestra, for whom Jenkins is currently writing his next major piece, "a combination of Kazhakstan folk tunes and what I do."

"John was very much involved in the recording of Requiem," says the composer. "And he's an excellent choral trainer. So I think we agree on how Requiem should sound."

Starts 2.30pm, tickets cost £20/£18, call 01273 465786.