It is, by anybody's standards, an arresting image: a truly beautiful photograph of a luscious, radiant creature, all shiny eyes and silky skin. And Greta Scacchi, who is pictured clutching the cod to her naked body, doesn't look bad either. In the months and years to come, this picture, flashed throughout the British media last week, will doubtless come to be seen as the seminal image for a particular moment, when the gruelling, knotty business of campaigning around food issues finally became sexy.

The use of celebrity skin to push an ethical issue is nothing new, of course. In the 1990s, Peta - People for the Ethical Treatment of Animals - convinced a bunch of supermodels, including Naomi Campbell, to appear in the buff under the legend "I'd rather go nude than wear fur". But fur is just so passé. And, in any case, Campbell proved just how fickle the modern celebrity can be by soon deciding that actually, come to think of it, she would much rather wear fur than go nude, and did so on the catwalk in Milan.

Where celebrities are concerned, it seems, food is the new fur. The current set of images featuring Scacchi alongside actress Emilia Fox, director Terry Gilliam and actor Richard E Grant, were launched to back the cinematic release of The End Of The Line, a film about the threat of overfishing - but they are only a part of it. Tomorrow, Paul McCartney and his daughters Stella and Mary are launching a campaign to convince the public to go meat-free for one day a week. Another movie, Food Inc, which looks at the excesses and foul side-effects of industrial food production has just been released in the US and will shortly arrive here. Plus there is a major investigation by environmental campaigner Tracy Worcester into the dark underbelly of the global pig-rearing business which is about to be screened on digital channel More4. Food, and more importantly, really bad food, is hot.

What marks out these campaigns is their sophistication. It began a couple of weeks ago with the news that Nobu, the global high-end chain of Japanese restaurants favoured by the glitterati, was still serving bluefin tuna despite it being an endangered species. The restaurant had added a note to its menu pointing out the threat to the magnificent bluefin and inviting diners to ask for an alternative, but had refused to stop serving it, unlike big-name chefs such as Gordon Ramsay and Jamie Oliver.

This was an old story; it had first been reported in September. It reared its head again because it features in The End Of The Line, the film version of a book by respected journalist Charles Clover.

Cue a letter from a familiar roster of celebrities - Jemima Goldsmith, Trudie Styler, Elle Macpherson - demanding Nobu remove it from their menus so they could eat at the restaurant with a clear conscience. Stephen Fry took to twittering about the issue. "It's astounding lunacy to serve up endangered species for sushi," he later said. "There's no justification for peddling extinction, yet that is exactly what Nobu is doing in its restaurants around the world." For its part, Nobu has refused to change its policy; apparently it feels it can do without the custom of Trudie and Stephen.

The producers of The End of The Line weren't finished, though. Clover had been discussing how to publicise the film with Nicholas Rohl and Elizabeth Bennett, friends of his who run the highly regarded ethical London sushi restaurant Soseki and who have helped pioneer sustainable fishing methods. "It was they who suggested getting celebrities on board," Clover says. "It was basically using celebrities to shame other celebrities and I'm rather keen on that."

Nicholas Rohl, who as well as co-owning Soseki is a screenwriter, has long known Scacchi. "I contacted her and she opened up her address book," he says. "It took us two or three weeks to set up. We sent out hundreds of emails and made hundreds of calls, but eventually we got the names together."

The photographer Rankin agreed to take the shots. Richard E Grant, pictured bare-chested with two feet of lovely, silvery, long-snouted fish, says he was motivated to get behind the campaign by his 30 years of scuba diving. "Commercial sea-floor dredging is an abomination," he says. "And free celebrity endorsement is the cheapest way to publicise an issue without wasting valuable funds, which are better spent on the cause itself."

Clover agrees. "The fact is that if you want to put an issue into the popular mind you have to get it into Heat magazine," he says. Scacchi even appeared on the Today programme to argue the case. "She's much better suited for doing something like that than me, and catches people's attention in the way I can't," Clover adds. But isn't it frustrating that, because of the way the media work, an actress who knows almost nothing about the subject is favoured over the man who literally wrote the book? Clover says not. "When you start hearing what you've been saying for five years in the mouth of someone who didn't know anything about it until five minutes before, it's awesome. It blows your mind."

Food writer and television cook Hugh Fearnley-Whittingstall, who has used his shows to argue for improvements in the way cheap chickens are raised in this country, sees nothing intrinsically wrong in non-expert celebrities getting involved. "What matters is how well they carry the message and whether they are in it for the long haul," he explains.

Nevertheless, there are bound to be some complications with celebrity-driven campaigns, not least the way they are, by habit, completely micro-managed. For example, Paul McCartney has sent letters to people in the media inviting them to a lunch tomorrow to launch his meat-free Monday campaign.

"Livestock continues to have a greater impact on climate change than the combined transportation sector," he writes. "This industry amounts to a huge 18% of the global warming effect - a terrifying statistic ... Help us to encourage the nation to reduce their meat intake by cutting it out just one day a week."

It sounds like an eminently sensible idea, but no more can be said about it, because the McCartneys have agreed an exclusive interview deal with another, unnamed newspaper and so will not talk to us, or anybody else for that matter, until tomorrow.

So why are all these campaigns happening now? Fearnley-Whittingstall believes the current burst of interest around food is a direct response to government inaction. "I certainly thought it was worth doing something like the chicken campaign, because government wasn't doing enough," he says. "If you want to save fish stocks or improve conditions for livestock, do you take it to politicians or do you take it to television and cinema? The latter seems the better way to work right now."

He credits Jamie Oliver with paving the way for campaigns like his, both by his efforts to improve school meals and his project to recruit jobless youngsters for his restaurants. "His shows marked a crossover for campaigning TV from dry documentary to more mainstream popular TV," he says. "The crunch question is to what degree the audience are converted."

It is a question Food Inc tries to answer. The feature-length documentary digs deep beneath the glossy, groaning piles of fresh produce in US supermarkets to reveal the less than appetising methods used to produce them - which have been held responsible for fatal outbreaks of e. coli and salmonella. The film is designed to be a wake-up call, its creators say. They include Eric Schlosser, author of Fast Food Nation, and Michael Pollan, author of In Defence of Food, who narrates the movie. "A lot of it is hard to watch," Pollan has said, "but I think people are ready to take a good, unflinching look at how their food is produced."

Naturally it comes with celebrity endorsement from the likes of US chef Alice Waters and lifestyle guru and sometime jailbird Martha Stewart, for no food campaign would be complete without that. But perhaps more intriguing is the 300-page book published alongside the film, full of essays on issues surrounding climate change, the environment and agriculture and offering advice on what consumers can do to make a difference.

"This is one of the most interesting social movements afoot right now," Pollan told Newsweek last week. "The politicians haven't quite recognised it yet. Hopefully this movie will be a part of the change."

Those who regard issues around food, which affect everything from the environment to healthcare and economic sustainability, as one of the greatest challenges currently facing the developed world will hope that he's right. They will also hope that no well-meaning celebrities have a Campbellesque change of heart and are caught feasting on bluefin tuna sashimi with a side order of baby panda rissoles any day soon.

They are what we eat

• Jamie Oliver has campaigned on many food issues. He caught public attention with his Jamie's School Dinners TV series in 2005 which campaigned to improve the standard of school meals. Jamie Saves Our Bacon this year highlighted the plight of many pigs reared in the UK and abroad.

• In 2008 Hugh Fearnley-Whittingstall presented Hugh's Chicken Run in which he created three chicken farms, one intensive, one free range, and a community farm staffed by volunteers.

• Eric Schlosser examined the global influence of the US fast food industry in Fast Food Nation, published in 2001. The book was made into a 2006 film, including graphic footage from a slaughterhouse.

• American film-maker Morgan Spurlock, above, demonstrated the health effects of McDonald's food in his documentary Super Size Me by eating nothing but the chain's meals three times a day, every day, for 30 days.

Caroline White