There was recently a cartoon in the New Yorker that had two men sitting in a publisher's office. One says to the other: 'As your chosen autobiographical ghostwriter, let me state up front that if I want any input from you I will ask for it.' I was reminded of this last week when it was revealed that Hunter Davies, formerly the biographer of William Wordsworth, was the new man in the life of Wayne Rooney.

The 20-year-old Manchester United striker, not best known for his erudite self-reflection, has signed the biggest book deal of the year with HarperCollins: five books for £5m. That signature will almost certainly be his sole written contribution to a lucrative exchange, which will span more than a decade. Davies will ghost the first of these tomes, with an option to do the second. (If he manages to do all five, a project that at the moment, from his point of view, must look a little like embarking on The Decline and Fall of the Roman Empire, he will be 82 by the time the final volume - Rooney: the Rotherham United Years - hits WH Smith.)

The Rooney deal highlighted the fact that the name on the front of any book on the bestseller list is increasingly unlikely to be that of its author. As in the film industry, writers these days take what credit they can; the billing goes to the star. If you were asked to name four of the hottest authors around your list should by rights include Rebecca Farnworth (who puts words into the mouth of Jordan, including two forthcoming novels), Tom Watt (David Beckham), Penelope Dening (Sharon Osbourne, Posh Spice) and Andrew Crofts (who has cornered the market in 'misery memoirs' with four number one bestsellers in two years). Ghostwriting is no longer the sector of publishing that dare not speak its name; it looks a lot like the future of the book trade.

It is at the very least a seductive arrangement for publishers who are desperately looking for sure-fire hits, ('Jordan' may well prove as robust a brand for flogging novels as Nancy Drew, say, or Mills & Boon), and with the kind of money involved it is hard for writers, relegated to the role of 'as told to', to say no. (Katie Price thanks her ghost, Rebecca Farnworth, in the small print of her latest book, in the same paragraph in which she thanks her 'accountant, Ali and [her] bank manager, David', which seems appropriate enough).

A month ago, when it was first announced that Rooney was in search of his amanuensis, Hunter Davies was happily scoffing at the absurdity of this project: 'Did the young Mozart get a five-book deal for £5m when he was only 20?' he wondered in a New Statesman column. 'Or Shakespeare? No chance. He was still hanging around the back alleys on his council estate in Stratford-upon-Avon, though he had met and married Anne Hathaway by then - without getting a penny from Hello! for the wedding.'

Davies knew exactly what lay ahead for Rooney, though, and had some words of warning. 'From my own experience of celeb biographies [Dwight Yorke, Gazza] I would say for the first book [Wayne] should allow three hours a day talking to his ghost writer, for six days, preferably spread over six months. That should do for the words, which he never need read ... The really knackering bit, Wayne, is to come ... Let's say five days of bookshop signings in London and the provinces; five days doing Richard & Judy, TV and radio stuff; then four days behind the scenes, glad-handing the trade ... I'd rather be tackled by Robbie Savage.'

Something about this schedule obviously appealed to Rooney, or to his publisher. In any case, as Davies revealed this week, he has been forced to revise his opinion slightly about the deal: 'Here's what's helped change my mind. I got this call from HarperCollins ...' Davies had been shortlisted to be Rooney's ghost. 'Eventually,' he recalls, 'I was called into the boardroom. There was Wayne's agent, Paul, an elegant woman I was told was his Brand Manager, another person in a suit introduced as his PR consultant, plus his own personal bodyguard.'

Davies neglected to mention his work on Wordsworth, though during the course of the meeting he remembered how, when he wrote the life of the great Romantic, he 'was effing and blinding, telling myself I'd never again write a life of someone who gets to 80 ... Took three years and I was knackered.' On the other hand, it was dawning on him: 'Writing the life of someone aged only 20 might pose certain, er, challenges.'

Rooney is not the youngest subject of a 'celeb biog'; Charlotte Church was only 14 when her ghost Jemima Hunt laboured over her first volume of memoirs, but it is probably fair to say he promises to be among the most taciturn. Rooney's sole contributions to the national discourse thus far have not extended beyond lip-read streams of expletives to hapless referees. When I mentioned Davies's Herculean task to other ghosts this week they took a sharp intake of breath as if imagining those days in front of a blank screen trying to summon up the secret diary of Wayne aged 133/4.

Douglas Thompson, who has adopted the voices of Christine Hamilton and Christine Keeler in the past, and recently managed to put himself in the tippy-toe shoes of Michael Flatley, suggested that the five Rooney books sound a bit more like 'novel writing than proper ghosting'. Eamon Dunphy, the combative biographer of Roy Keane, offered the thought that the book has gone to the wrong man. 'Hunter is a pretty dodgy fucking writer, though Wayne is a good lad, so it may turn out OK.' He suggested Rooney should watch his back. 'The thing about Hunter Davies is I'm not sure who's side he's on, he really turned Gazza over in that book, he was absolutely savage. I just hope Rooney knows what he is letting himself in for.'

The term ghostwriting was coined by Christy Walsh who formed the Christy Walsh syndicate in 1921 and for years controlled the literary output of American sportsmen from Babe Ruth to Bill Tilden. His ghosts included the young Damon Runyon. Walsh, a fierce Irish republican, established a strict code of conduct for his operation. Number one was: 'Don't insult the intelligence of the pubic by claiming these men write their own stuff.' Number two was: 'all ghosts must be in daily communication with their "bodies".'

Babe Ruth in particular was his prototype Rooney. Walsh sold three volumes of autobiography of the baseball legend for vast sums of money, as well as a long-running weekly syndicated column. Everything he learned about ghosting he learned from his experiences with Ruth. 'A new ghost writer has to learn a lot about style,' he suggested. 'He usually makes the mistake of thinking that he ought to write the way his celebrity talks. That is an error. He ought to write the way the public thinks his celebrity talks.'

In the gap between those two voices lie all of the ghost's creative possibilities and all of his worst nightmares. Whenever my bank balance appears to tempt me toward ghosting, I'm haunted by the story of an indefatigable ghost who used every desperate resource to make it to the end of his contracted 70,000 words about a particularly prolix Yorkshire cricketer. No routine catch at midwicket or unsuccessful lbw appeal was left unexplored. There were paragraphs about the sound of birdsong at various county grounds, and about favourite groundsmen. When he delivered his manuscript and felt the burden of word-count despair briefly lift from his shoulders, he received a call from his publisher. 'This is terrific stuff. Do you think you can do another 30,000 words?'

Cricket's original hero, WG Grace, employed a writer called Arthur Porritt, who described exactly the 'Rooney dilemma', the one which states that great sportsmen do all of their talking on the field: 'Getting material from Grace was almost heartbreaking,' he recalled. 'All he would say in recording some dazzling batting feat of his was "Then I went in and made 284".'

Eamon Dunphy, who wrote perhaps the best ever footballer's memoir Only a Game? (with a little help from a journalist called Peter Ball) admits he might just have been tempted by the Rooney magnum opus, but that really he would not have ghosted a book for anyone but Roy Keane (for which he received £250,000 and a few nominations for book of the year). 'A decent sports book is a great rarity,' he says. 'There's something about the whole thing that is so bogus. It is particularly difficult to capture what is authentic about the subject with the subject there breathing down your neck.'

The thing is, Dunphy suggests, 'author' and ghost are generally approaching their task from very different places. 'Their commitment is to their sport whereas yours should be to your reader.' This was not the case with Keane. 'Roy hated the fakeness of football books, like he hates the fakeness of everything. He wanted to be honest about the way he was drinking, about what he thought of other players and so on.'

Dunphy says publishers are 'mad for this stuff now'. He's had a lot of offers, reportedly had a sniff of the coveted Mourinho ghosting. 'It is all to do with this kind of voyeurism,' he says.

It seems to me that such books are rather a last resort of wish fulfilment. We invest so much of our culture in sport and celebrity that it feels necessary that the principal players have something to say for themselves. The soundbites you hear on Sky Sports News, or the quotes that are reheated in Heat will never be enough. The frustration of celebrities is they are in a world we desire but are unable to articulate how we imagine it feels. That's why the ghost - who exists in a hinterland between reality and surreality - is so engaging. He or she provides a voice that is halfway between his or her mundane life - and therefore ours - and that of the subject.

The most compelling deconstruction of this curious three-way relationship came in Jennie Erdal's book Ghosting, in which she dissected her 15 years of working for the tycoon Naim Attallah. Her role was to create her megalomaniac boss's public voice and to this end she wrote, on his behalf, newspaper articles, speeches, letters to editors, declarations of love and a dozen books, including a series of interviews and two novels.

'The word "ghost" was never mentioned between Naim and I,' she says. 'There is usually a contract between the author and the ghostwriter. In my case there was none of that.' She saw her primary role as protecting a man's illusions about himself. 'This was someone, you have to remember, who could not read let alone write his own work in English.'

Attallah's was an extreme case of that modern pathology which states: I could be a great writer if only I had the time. Like all non-writers he could never work out what took his ghost so long; it was only typing after all. Though Jennie Erdal was assuming his voice, she says she still had to raid all of her own life for stories. 'Nearly everything that is in the novels has some personal connection with me, apart,' she hastens to add, 'from the sexual requirements, of course.'

The hardest thing was always maintaining the pretence that her boss was the one actually doing all of it. 'At a very deep level I am sure he believed that,' she says. When Ghosting came out and revealed the truth, she believes Attallah's illusions were 'jolted but not destroyed'.

This tendency is not uncommon amongst celebrity authors who frequently don't need too much persuading of their literary achievements. After paying her ghost Camille Marchetta $350,000 to write a novel about a Czech alter ego named Katrina, Ivana Trump, for example, seemed to have convinced herself of her gift. 'To my surprise, I find I have a great imagination,' she told -Vanity Fair in her unwieldy English. 'I don't say I'm the Shakespeare, but it's not just about the beautiful people and the gorgeous yachts and the fabulous homes and lots of sex. I tried to put in more the feelings.'

The temptation is infectious. Naomi Campbell's publisher repeatedly refused to admit that the model's novel Swan was the effort of a ghostwriter, though Campbell pretty much admitted it herself. David Beckham meanwhile happily accepted awards for 'the autobiography what I wrote' and Madonna neither confirms nor denies the reports that her children's books, which she donned her donnish specs to promote, have been partly the work of Kabbalah's 'in-house' ghostwriter Eitan Yardeni.

The more serious the 'author' the more assiduous the attempt to maintain the illusion. Mark Twain is said to have ghosted Ulysses S Grant's memoir, but neither owned up. By some accounts André Malraux brought his style to the life of de Gaulle. In the acknowledgments to her vast memoir, Hillary Clinton belatedly named the three writers who had 'guided my efforts' but gave few clues when confronted with the question of who wrote what. Ronald Reagan was perhaps alone in having no such qualms. 'I hear it's a terrific book,' he said of his autobiography, ghostwritten by Robert Lindsey. 'One of these days I'm going to read it myself.'

After she left Naim Attallah's office Jennie Erdal spent the first year as 'a recovering ghost' and wrote her memoir partly as therapy. She is currently writing the novel of her own that she had always planned. Without the echo of Attallah's voice and the tyranny of his deadlines she is, now, like most proper writers, plagued by doubt. What seems good in the afternoon no longer looks right in the evening and is often deleted by the morning.

Recently when searching for something else on her computer she came across a series of files that were early drafts of the novels she wrote for her former boss. 'I must admit,' she says, 'reading them I got myself into a very bad state. I just had an overwhelming sense of having squandered so much of my creativity for this man. And then I wondered if there was some use I could put some of the material to, but I suppose I might be accused of plagiarism if I did so ...'

The key quality of any ghost, Andrew Crofts suggests, is the absolute absence of ego; since this is not a trait often associated with writers, good ghosts are hard to come by. 'Most writers have ghosted, or will ghost or would like to ghost, but very few writers would ever think of themselves as ghosts,' he says. Crofts, who is 53 and lives in Sussex, is widely acknowledged as the modern master of the genre, though he is of course too self-effacing to make that claim. In the 15 years he has been ghosting full time he has written 60 books that have collectively sold perhaps 10 million copies (he's lost count).

He's done a few celebrities, Gillian Taylforth, Benvenida Buck. He wrote Crocodile Shoes for Jimmy Nail. But mostly he is the 'ghost of real people with extraordinary lives'. These include the Birmingham teenager Zana Muhsen, who became an enforced child bride in the Yemen, (Sold, the result of their collaboration, has sold 4 million copies worldwide) as well as several confessionals from abused children, among them Kevin Lewis's The Kid and Jane Elliott's The Little Prisoner.

Crofts reckons that he can sit down with most of his subjects for a couple of days and get pretty much the whole story on tape. 'Mostly it's a question of getting how it looked to them. If someone has been whiteslaved, say, you want to know exactly what the airport looked like, for example.' He imposes a structure, usually a redemptive one, or at least he tidies things up, 'otherwise life would be just one rambling computer blog'.

When he shows his subject 'their' book the reaction, he suggests, is often the same. 'It's like if someone has taken a photo of you at a party. When you first see it you might not like it at all. But then you realise fair enough, that's probably what I look like.'

I wonder if he ever loses the distance between himself and his subject? When he writes, he says, certainly he finds himself disappearing into the voice. His wife tells him that he often starts talking like the people he is writing about; if he's knocked out 5,000 words a day he'll come down in the evening with a bit of a Brummie accent or whatever. 'She got really worried when I was doing Lorraine Chase,' he admits. This identification extends to a relaxation of moral judgment. 'If I'm writing about someone who is morally dubious, I'll find myself fiercely defending them if someone criticises them. You have to see things entirely from their point of view. Being a ghost is a bit like being a therapist,' he says. 'But it is probably more like being a defence lawyer.'

James Morton, who has been both ghost and lawyer, agrees there are plenty of similarities. As a solicitor Morton acted for 'Mad Frankie' Fraser after the Parkhurst riots. When Mad Frankie was released he went back to his lawyer to see if he'd do his book.

Morton was intrigued partly, he says, because as a defence brief you never really ever get to hear the truth. 'Once I'd retired I could talk to some of these men and find out what really had gone on.'

Not surprisingly, he felt in his case it was essential to keep a little distance between himself and his subjects. 'I'm not one of those who would want to spend a lot of time in public houses with either criminals or policemen,' he says. With Fraser, for whom he has ghosted five books, it was all pretty straightforward. 'I'd say "bank job" and he would sit at his kitchen table and tell me about it. I'd take out the repetitions and that was that.'

Morton's Fraser books happily broke Christy Walsh's third law of ghosting, that of writing in the actual voice of the 'celebrity'. Fraser was good enough a storyteller to let Morton get away with this, but his idiom created the voice of the true crime 'industry' nicely parodied by Martin Amis in Yellow Dog. 'Regarding the matter of giving your mates' wives one,' Amis's ex-con explained to his ghost. 'Now in them days that's considered not on. Something you don't do - but what's the bloke going to do? Come round and have it with me about it? No they gives their wife a biff and otherwise and that's it. End of story which they thoroughly deserve.'

Morton is unrepentant about this particular contribution to the culture. 'There's no way of saying this that doesn't sound pompous,' he says, 'but first and foremost I regard these books as an important bit of social history.'

He puts the current vogue for ghosted celebrity memoirs and footballers' lives in the same category. The Rooney books will tell us a lot about how we live, what we fantasise about. 'The thing is you mustn't decry anything that people read,' Morton suggests. 'For some people these kinds of books might be the first book they have ever picked up. I like to think that there's a reader out there who started with Mad Frankie Fraser and has now graduated to Zola.'

I assume he means Émile, not Gianfranco.