Pop stars are earning a crust - and, in some cases, their bread and butter - from business ventures including restaurants, films, fashion, and pit-bull farms. How do they find time for music, asks Jim Carroll

ONCE UPON A TIME, the pop maxim used to be "where there's a hit, there's a writ". Now, it's more likely to be "where there's a hit, there's a lucrative range of ancillary gigs for the artist to exploit that have absolutely nothing to do with music".

It may not quite roll off the tongue in the same way, but the phenomenon has resulted in large sums of cash rolling into the bank accounts of many pop acts.

The extracurricular activities of pop stars have resulted in some staggering business stories. For instance, Jay-Z recently trousered $204 million (€152 million) for selling the rights to his Rocawear brand - where annual sales are north of $700 million (€520 million) - to the Iconix Brand Group.

The fashion hook-up is an obvious one, especially as the pop star can see the cash coming his or her way from retail sales of everything from T-shirts to shoes. It's like a super-scaled version of the merchandise stall at the back of the concert hall.

But for the brands, retailers and designers who sign up pop stars and their fashion sense, it's the marketing and association that matters as much as the ringing cash registers.

Madonna's recent dalliance with Swedish fashion giant H&M for her M by Madonna range, for instance, may well have reflected the singer's "timeless, unique and always glamorous style", to quote the press release, but it also strengthened H&M's position as a streetwise brand capable of attracting fashion and pop's leading lights.

After all, Madge could have hawked her kimono dresses, skintight pants and pencil skirts to Wallis or Principles, but she went with the high street cool of H&M instead.

You don't have to wait until you have a couple of dozen hits and a few husbands under your belt, either, to start badgering designers about the length of the hemlines on your capsule collection. Lily Allen's Lily Loves range of dresses, shoes and accessories will be going into New Look stores next month.

Allen demonstrated that she has the art of promotion down pat by having a go at Kate Moss, ensuring plenty of column inches for the Lily Loves launch. Of course, the fact that Moss is currently prepping her own clothing range for Topshop had absolutely nothing to do with the spat.

It really does seem as if every pop star in the charts also has a fashion line of their own to flog. If you're inclined, you can wear clothes designed in one way or another by Beyoncé (her House of Dereon is "a place where couture crosses cool"), Gwen Stefani (L.A.M.B.), Justin Timberlake (the William Rast range is about bringing sexy back, albeit with clothes that look a bit like Abercrombie & Fitch castoffs), Jennifer Lopez (Sweetface) and Jessica Simpson.

Less mainstream acts are getting in on the act too. Earlier this year, Lee Jeans launched a series of T-shirts designed by Bloc Party, Doves and Kaiser Chiefs, while US company Lyric Jeans hooked up with KT Tunstall for a T-shirt and belt inspired by Marvin Gaye's Mercy Mercy Me, Earth Day, global warming and pollution. You have to wonder if all that designing is having an impact on the quality of the music-making.

Fashionistas will argue that there's nothing new about any of this: pop has always had the hots for fashion. Back when punk first bared its claws, the Sex Pistols were first and foremost promoting Malcolm McLaren and Vivienne Westwood's London shop Sex. In return for bondage trousers, safety-pin T-shirts and assorted other clobber, the Pistols spread filth and fury and advertised their Svengali's shop on London's King's Road at the same time. Everyone was happy.

But pop stars no longer confine themselves to the changing rooms when it comes to brand extensions. Be it Justin Timberlake's investment in restaurants in New York and Los Angeles or U2's Bono and The Edge investing large wads of cash into Dublin's Clarence Hotel (like the band, we're keen to forget all about their Mother record label), the sidelines of the rich and famous make for a varied and interesting balance sheet.

One genre above all others has recognised the cash potential of sidelines.

Almost as soon as a hip-hop act has a multi-million selling album under their oxter, the extra stuff starts coming hard and fast. While P Diddy leads the pack (see panel), 50 Cent isn't far behind. He has turned into the Hector Grey of hip-hop, with a portfolio that includes the G-Unit record label, books, clothes, video games and bottles of vitamin water.

He also starred in Jim Sheridan's Get Rich Or Die Tryin' flick, which showed there's at least one sideline he should remove from his CV.

One potential area Fiddy could explore is the dog business, but he'd then be stepping on the toes of the mighty Big Boi. Last year, the OutKast rapper talked to The Ticket about his pit-bull breeding business at Pitfall Kennels outside Atlanta.

"I've about 80 to 100 on the farm now. We're booming. I've thought about greyhounds and about getting into the horse business. It's fly to have a horse and all that, but they win serious money too and then there's the stud fees afterwards."

P Diddy, Mr Busy

Unforgivable (a men's fragrance launched with Estée Lauder, retailing for $75 a bottle)

Sean John (the clothing range has annual sales of $400)

Sean by Sean Combs (women's clothing range currently on a hiatus)

Bad Boy Records (he sold a 50 per cent share in the label's catalogue to Warner Music for $35 million)

Justin's (Caribbean and soul food restaurants in New York and Atlanta)

Blue Flame (marketing and advertising agency)

Sean John Navigator (a limited edition Lincoln SUV priced at $85,000)

Daddy's House (New York recording studio)