CAN YOU MATCH THESE FAMOUS FACES TO THE PRODUCTS THEY ADVERTISE? (ANSWERS BELOW); 4 `Very few people will say no to pounds 50,000 for a day's work' 4
"that photo is Michael Portillo, and he doesn't advertise anything at all. This is a trick question, isn't it?" snapped the businessman on the station platform suspiciously. Well, erm, no - actually it's Will Carling, and he promotes the myco-protein meat substitute Quorn. "I've never heard of it. But I know Michael Portillo when I see him," insisted the man.

Ad agencies hope that we do know famous people when we see them - in fact, they bank on it. They pay celebrities fat fees to endorse their products - payments start at around pounds 50,000. But is forking out for a star always cost effective? Confronted with mug-shots of well-known product- floggers, some punters, the advertisers' dreams, confidently link Hale and Pace to Clorets mints, Jane Asher to McVitie's biscuits, and Cindy Crawford to Pepsi. Others, however, are totally blank.

"This might be Pamela Anderson," said a baffled woman, poring over Cindy's picture. "I don't know what she advertises. I know these are the Birds of a Feather - they do a soap powder, but I can't remember which one. Persil? Daz?" In fact it's Surf. "Oh."

Earlier this year, advertising analysts the Planning Partnership conducted a survey for Marketing magazine to find out how well people absorb advertising fronted by a well-known face. It asked punters if they could remember which products were associated with 32 different personalities. 77 per cent of their sample remembered that Bob Hoskins advertises BT but only three per cent knew Dawn French had appeared for Racal Vodaphone. "The critical question for marketing people is whether viewers will remember the personality rather than the product - it's a great source of paranoia for them," says managing director Barry Pritchard. "And frankly, nobody really knows the answer."

So what's the magic ingredient of the BT Bob Hoskins campaign? "A pounds 50m spend," says Mr Pritchard bluntly. "BT are the biggest, and it works. It's Pavlovian - if you have adverts absolutely everywhere, people are bound to take them in."

It's confusing if the same face is pushing fairy liquid one week and old-fashioned cider the next. "Some personalities do multiple campaigns, like Julie Walters, who's done Clorets, Imperial Leather and Harvester, and that's definitely bad," says Mr Pritchard.

If he were launching a new product, would he rush to secure a celebrity endorsement? "If it was a crap product - that's what people do. In fact, we've found that recall of animals like the Andrex puppy or the PG chimps is much higher than recall of human stars."

But among those who decide to stick to a human face, who decides that Cindy plugs Pepsi, while Sharon and Tracey shift Surf? Bringing together celeb and product is evolving into an industry in its own right. Max Markson is managing director of Markson Sparks!, a company that specialises in "personality management". He believes that the cult of the famous product-endorser has hardly got under way yet. "America's been doing it for years, so has Australia, and I think that Britain is going to explode as well."

Markson Sparks! has a large assortment of sports stars available. "When an agency rings us to say they need someone to promote such-and-such a product, I'll bounce a few names off them, and if they want someone who I don't represent already, I'll get in touch," says Max Markson. "The personalities are all keen to do this kind of work. Well, if someone says to you: `Do you want to earn pounds 50,000 for a day's work?' few people will say no. The magic is that there are so many ads on television, getting a well-known face grabs viewers, makes them say: `What's that personality flogging?' " His campaigns include Graham Gooch's new head of hair for Advanced Hair Studio, and the British Girls of Sport calendar, featuring swimmer Sharron Davies.

Alternatively, ad makers can create their own stars - supermodel Eva Herzigova was unknown before she stripped off for the Wonderbra ads. Other promoters even claim that the star is all-important and the product takes second place, such as Nike's current campaign, featuring footballers Eric Cantona and Les Ferdinand talking about racism. "We wanted to bring something to the game rather than just trying to sell boots to the players," explains Peter Bracegirdle, account manager at Simons Palmer, Nike's British ad agency. "Nike has a very strong relationship with the sportsmen who promote the goods - it's not just a question of `Here's the cash, wear our boots.' It's not a glamorous ad, and it's not heavily branded - it's almost a Nike sponsored message."

Nike had to hold back their campaign when Cantona was on trial for kicking an abusive fan; promoters have to hope their chosen face behaves, as any adverse publicity may rub off. "It's a risk you take," says Dominic Mills, editor of Campaign magazine, which monitors the advertising industry. "Look at Michael Jackson, who did Pepsi, or OJ Simpson, who was Hertz cars."

Big names are viewed with some ambivalence by the ad professionals. "If they're relevant to the ad then it's fine," says Dominic Mills. "But if you just throw in a celeb for the sake of it, it suggests you haven't got an idea. If you use someone that has nothing to do with the product and the viewer has to work too hard to work out the connection, it's no good - or if their personality overwhelms the product." Joanna Lumley, he says, is a prime example.

Is it possible that a high recall score is based as much on sheer irritation, or even hatred? "There's always a danger of celeb wear-out," agrees Dominic Mills, "but the media schedule is planned in such a sophisticated way that unless you are a very sad person that never goes out you shouldn't see the same ad more than five or six times - you'll see the same product, but you should see different treatments."

Sportsmen are the flavour of the month. David Platt has just started advertising for McDonald's, who have announced a major sponsorship deal with the football Premier League. "I've been one of McDonald's best customers for years," commented Platt dutifully. He is jumping on to the same bandwagon as Cantona (Nike), Will Carling and Ryan Giggs (Quorn) and Gary Lineker, who reportedly received pounds 750,000 for lending his name to the promotion of ... well, can you remember? But sometimes the fame comes later on: Michael Portillo was a schoolboy when he appeared in a Ribena ad.