The Big Question: Why are so many political memoirs published, and does anyone read them?

Why ask now?

Because poor old Gordon Brown, as if he hasn't got enough on the his plate, is facing an onslaught from three different sets of memoirs, which have been released in recent days, by Cherie Blair, John Prescott and Lord Levy. All of them have unhelpful things to say about the Prime Minister's personality and behaviour.

Why do people write them?

The Americans have a term for it. They call it "legacy writing". It includes any memoir-writing for recreational, family or therapeutic purposes and it certainly covers the self-serving, self-congratulatory style of many types of political writing.

Often the writer wants to produce an apologia which will set right their place in history. Sometimes they are animated by a sense of having been wronged – as with Lord Levy, who feels hard-done-by, or Cherie Blair, who had grudges to air about Gordon Brown and various others.

Some writers just feel overshadowed – which perhaps explains why no fewer than 18 former members of Margaret Thatcher's cabinets published memoirs. Some were very long, such as Nigel Lawson's massive 1,100 pages. You can glance along the political bookshelves at others – Michael Heseltine's Life in the Jungle, Jim Prior's A Balance of Power, Geoffrey Howe's Conflict of Loyalty or Douglas Hurd's imaginatively-entitled Memoirs – without the spark of memory igniting. Others, such as the autobiography of Norman Lamont, are remembered by political correspondents for their extreme tedium. Yet others offer only ammunition for political tittering, such as Norman Fowler's The Minister Decides (the only thing Norman never did, quipped one wag). Most of these sold only a few thousand copies. The other reason that people write political memoirs is for the money.

Do they make any money?

Well, Cherie Blair reportedly got £1m for hers – not quite the £4.6m her husband landed for his, but not bad for a few months work. Tony Blair had been hoping for £7m from the auction for his book, which was conducted by the US lawyer Bob Barnett, who secured big advances in America for the memoirs of Bill Clinton and Alan Greenspan. But it became clear that the market had fallen; some even blamed Mrs Blair's deal, with industry pundits wondering whether her revelations might take the sting out of his.

His yet-unwritten book was eventually bought by Random House whose chief exec Gail Rebuck is married to Mr Blair's former pollster, Philip Gould. On securing the deal, she said: "He was an extraordinary prime minister, and this will be an extraordinary book".

But she must know that the two things do not go hand in hand. Interesting Harold Wilson produced a book of stultifying dullness, full of lists of everything he did every day of the week. Whereas boring old Ted Heath produced one of the best political memoirs of that era, full of brilliant anecdotes about how he met Hitler's cabinet after a Nuremberg rally and revelations such as that, at one point during the Northern Ireland troubles, the Cabinet had a naval fleet stationed off Londonderry.

Does anybody buy them?

Three kinds of books sell, according to Joel Rickett at The Bookseller. The first are books by prime ministers. Baroness Thatcher's Downing Street Years sold a massive 500,000 copies and even dull John Major sold 200,000 in hardback. Tony Blair can expect to sell somewhere between the two, industry analysts predict, though he might do better abroad than even Mrs T.

The second set of sellers are books which are published very speedily after the event: the heavily censored diaries of Blair's spin doctor, Alastair Campbell, sold 70,000 copies in less than two months and the spit-and-tell memoirs of the former Washington ambassador Sir Christopher Meyer sold well. But books by other Blair ministers, including Robin Cook and Clare Short, all disappointed. And David Blunkett's – which got a £400,000 advance – flopped, selling a measly 4,000 copies.

The third set who sell well are individuals with a hinterland outside Westminster. The Speaker Betty Boothroyd sold 106,000. The plain-speaking Mo Mowlam sold 40,000. Tony Benn has sold solidly with the eight volumes of his diaries. The waspish Thatcherite diarist Alan Clark appealed to a wider public as a party disloyalist as well as a roué – and diaries often sell better than memoirs because they have the freshness and candour of instant history written by people who do not know the ending rather than the reworkings of hindsight.

What about press serialisations?

Newspapers buy up political memoirs to serialise them. The current going rate is between £50,000 and £200,000, considerably down on previous eras. Publishers aim to recoup from these lucrative serialisations between 50 and 100 per cent of the advance they pay the author. If the author does not deliver the dirt as promised, the inkies renegotiate the fee.

Serialisations can be a two-edged sword. David Blunkett's eagerly-awaited diaries were so exhaustively extracted that many people felt there was no need to buy the book because they had read the best bits – his catty comments about Cabinet colleagues. Or it may have had something to do with the fact that he made no admission of the sexual shenanigans which spurred his downfall. There was not even a mention his high-profile affair with Kimberly Quinn.

Do any of them tell the truth?

Hmm. Most are exercises in self-justification. Some, like Alastair Campbell's, pull all their best punches. Others deliberately rewrite history. Cherie Blair's claims that the reason Tony didn't stand down at one point as he promised Gordon Brown was because he was afraid Brown would abandon his health and education reforms on foundation hospitals and city academies.

Insiders know that is untrue. Blair had thought the game was up and that the Hutton or Butler reports would point the finger at him. When they didn't, beyond a few imprecations about sofa government, he told Gordon Brown that he couldn't step down now because if he did everyone would assume that he was guilty after all.

The most truthful book on the New Labour project is said to be Philip Gould's The Unfinished Revolution.

So what is the best way of reading them?

With a beady eye. Anything which makes the reader say: "He would say that, wouldn't he?" can be discounted or ignored. Anything which doesn't reveal the author in the best possible light is probably true. Caveat emptor.

Are political memoirs worth reading?

Yes...

*Diaries particularly can have a freshness and candour that are rewarding to read.

*They always seem to reveal political life to be far worse than the public supposes.

*If you read enough of them, you discover the truth somewhere in the middle.

No...

*The worst ones are self serving, self-justificatory and self-congratulatory.

*They omit anything which casts the author or any of their close political allies in a bad light.

*All the best bits appear in the newspapers and interviews beforehand anyway.

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