Shot one. The actor Colin Firth sits at a desk, hands clasped, wearing a long- sleeved T-shirt as dazzlingly white as Britney's teeth.
Shot two. Open-mouthed, Colin looks as though someone has just poured a cup of cold coffee over his head. Someone has.
Shot three. Coffee coming in torrents now.
Shot four. Coffee slows to a trickle. Colin scrapes his sodden hair out of his eyes.
This is what a celebrity with a conscience faces nowadays. And Firth is not the only one to suffer. To promote Oxfam's Make Trade Fair campaign, Jamelia agreed to be buried in feathers, Coldplay's Chris Martin said yes to a mountain of rice, and Antonio Banderas sat under a shower of corn kernels. To be strictly truthful, the kernels were more of a trickle than a deluge, but he hammed it up like an am-dram veteran.
Firth was trying to underline the point that 25 million coffee growers face ruin because they don't get a decent price for their crop. Martin's ordeal by rice stressed that the US government pays farmers $1bn a year to overproduce rice and dump the surplus at rock-bottom prices in poor countries. Jamelia's feather bath was to publicise the way poor countries are smothered, losing $2 through trade for every dollar in aid they receive. The interesting question is not so much why these celebrities do what they do for campaigns such as Make Poverty History and Make Trade Fair, but why we expect them to do it before we pledge our money.
The market research company Mintel has just reported that three out of five adults are "bored with celebrities" and a further one in five is "celebrity-resistant". Is this likely to make us shun such high-profile charitable campaigns? Oxfam doesn't think so. Its celebrity co-ordinator, Claire Lewis, says that once the pictures of drenched stars were released, the organisation's Make Trade Fair website got more than a million hits. Stars were chosen to appeal to fans across the world, with Antonio Banderas scooping up Central and South America and the pop duo the Finn Brothers appearing on magazine covers in New Zealand and Australia.
Sharon Stone underlines the point. The actress leapt to her feet at the World Economic Forum in Davos, Switzerland, in January, pledging $10,000 of her own money to buy mosquito nets for Tanzanian children at risk of malaria. She then exhorted the audience to "just stand up, just stand up. People are dying . . . and that is not OK with me." In five minutes she raised $1m. It was a staggeringly successful example of a celebrity seizing the moment and forcing people to follow.
As Germaine Greer knows, it doesn't always work. She stalked out of the gilded cage, otherwise known as Channel 4's Celebrity Big Brother, saying she had only gone in the house in the first place to raise money for the Australian rainforest. It had, she said, "earned me a lump of cash that will be the rainforest cushion". But it turned out to be her own land she was trying to restore. Similarly, the BBC Breakfast news presenter Natasha Kaplinsky faced questions about the precise amount she gave to charity after being paid to appear on Strictly Come Dancing. The lesson is that if there is even the slightest hint of self-interest or self-aggrandisement - or any attempt to boost a flagging career - in a celebrity's endorsement of a charitable cause, both the star and the cause get a kick in the shins.
Victoria Beckham pre-empted the criticism when she visited Peru. "There are bastards who'll think, 'There she goes with her Mother Teresa act'," she said. That's exactly what people did say, given that the trip coincided with tabloid allegations about her husband, David. Sometimes the relationship bet-ween star and charity is too symbiotic for comfort.
The man who unleashed the concept of celebrity endorsement was Bob Geldof. His prototype was seized by the likes of Bono and Chris Martin. The Coldplay frontman is as pragmatic as you can get about his involvement in the fair trade campaign. "It's just the same as when you see . . . Britney Spears advertising Pepsi . . . I'm confident in the product we're advertising, so I have no need to be nervous." In Mexico, Martin was photographed behind a plough. "I know full well that you have to kind of whore yourself around. But we don't care about looking like idiots . . . We look totally stupid standing behind a plough. But that doesn't matter as long as you get the words 'make trade fair dot com' in the newspaper."
And that is the really tricky part: getting it in the newspaper. The people being helped do not always appreciate being "in the newspaper". As a BBC news reporter, I was sent to film the actor Jeremy Irons and the journalist Libby Purves pretending to be homeless for the night. They climbed into their cardboard boxes. No problem - until a group of genuinely homeless young people marched over to have a word. They demanded to know whether the stars would be going to the Ritz in the morning for a bath and a good breakfast. The entire acrimonious conversation was captured on film, much to Purves's embarrassment. But she, Irons and I were in it together. They were trying to show sympathy for the homeless, but just looked smug and self-indulgent. I was capturing famous people on camera for the entertainment of the early-morning TV audience. None of us came out of it with much credit, and the homeless came out of it with nothing at all.
Only one person can truly be said to make a difference to public opinion in a unique mix of icon, pan-world celebrity, elder statesman, benign grandpa and political activist. There is no one to touch him. Geldof introduced him in London on 3 February as the man "with the coolest shirt collection in the world". Obviously deciding that "universal shirt leader" was not praise enough, he went on to describe him as "the president of the world". Would you like to see Nelson Mandela sitting behind a desk, hands clasped, in a long-sleeved white T-shirt, waiting for cold coffee to land on his head? I wouldn't. But will there come a time when we expect it of him, too?
We are a fickle lot, and one charitable cause can swiftly displace another. Look at the socially conscious wristband: as causes proliferate, we're running out of colours to use to promote them. You wear a yellow band for Lance Armstrong's cancer foundation. But yellow can also signify Support Our Troops. Blue means you're anti-bullying, supporting tsunami relief or fighting prostate cancer. Orange helps those with Asperger's or fights self-harm. Red is risky, because you're either anti-tobacco or pro-George Bush. Fair trade doesn't have a wristband (yet) but it has plenty of T-shirts, including the "metal regular tee" and the "zinc vest". Charities have become skilled at getting our attention. Perhaps we should all grow up, scrap the stage effects, dump the wristbands and T-shirts and actually listen to what people have to say.
