The first Jeffrey Archer I met, Jeffrey Mark One, was a trainee PE teacher. He arrived at my prep school in 1964 to give weekly sessions to the First XI soccer side - and a cracking good job he did too, memorably committed to the task of getting 12-year-old boys fit.

The earnestness and passion with which he got us to do intervals of sprint-jog imprinted upon me a technique I went on using for years. We were sufficiently keen on him at the time for our choir to sing at his wedding.

I met Archer Mark Two in 1987 when I interviewed him for a TV programme. Until recently, this Archer had been deputy chairman of the Conservative Party, a role he had resigned in order to fight the Monica Coghlan libel trial - the one at which, it emerged last year, he perjured himself.

I warmly thanked him for teaching me how to get super-fit all those years ago. He looked blankly at me. When I tried to prompt his memory, he seemed to have no idea what I was on about.

I do not know if he was genuinely unaware of his previous role or whether he was pretending not to know. Archer is both a fantasist and a liar, so it could be either. In reading his diaries one is constantly struggling to tease out where the manipulator begins and the Toad of Toad Hall, Walter Mitty self-deluder ends. Above all, there are different fantasies he is having about himself, differing dramatic roles he enacts.

The persecuted writer

'When I get out, will I have to follow the path of Oscar Wilde and live a secluded life abroad, unable to enjoy the society that has been so much a part of my existence?' Archer probably suffers from what is known as a Borderline Personality. Lacking much sense of self, he evades disintegration by adopting personae that give him identity.

Such people often feel at their most real when living 'as if'. They are safer with pretence than reality, living more fully when experiencing in inverted commas: 'Jeffrey Archer' (The Great Novelist, The Important Politician) in a role in a narrative that he may narrate to himself in his head ('Archer woke in his lonely cell to face another bleak day... ', rather than just plain old J. Archer, someone who is very unsure of who he is).

A recurring persona in his diary is the persecuted, misunderstood author whom the authorities have wronged. He rails against Mr Justice Potts for judging his trial unfairly; likewise his treatment by the prison authorities.

Whether or not he has read Oscar Wilde's poem 'The Ballad of Reading Gaol', written after the author was incarcerated for homosexual acts, Archer hopes that by associating himself with this great and tragic writer he will evoke sympathy from readers. The fantasist is probably unaware there is no basis for comparison.

Whereas Wilde was a great author who was treated despicably, Archer is a potboiler-writing conman who got his just desserts. After several investigations of his financial dealings, he is probably lucky to have been convicted only of perjury. Manipulator Archer knows this, the fantasist believes he is comparable to Wilde.

The criminologist

'There is a child of 17 in the cell below me who has been charged with shoplifting - his first offence, and he's only on remand, not even convicted - and he is being locked up for 18-and-a-half hours, unable to speak to anyone. This is Great Britain in the twenty-first century: not Turkey, not Nigeria, not Kosovo, but Britain.'

Archer adopts the persona of a sanctimonious prison reformer, raging against the iniquities of the system. He forgets he was a close friend of the two Prime Ministers largely responsible for what he is describing, that it was Margaret Thatcher who said 'Blow away the fog of excuses... only the criminal is to blame' and who deliberately increased the prison population to bursting point.

Archer the criminologist is suddenly an authority on prison conditions and the need for radical reform. With astonishing egotism, he aggressively instructs the powers-that-be as to their duty.

'I do hope the Home Secretary - who I know to be a decent, caring man - will read this carefully.'

After each gobbet of what he regards as startling new evidence of prison life, he barks an italicised command at Blunkett:

'Home Secretary, this hard-working family man is fearful for his safety. Is that what you're hoping to achieve for someone who's been caught driving without a licence?... Home Secretary, you are doing irreparable harm to decent people's lives and you have no right to do so... Pay attention, Home Secretary... I hope you're still paying attention, Home Secretary.'

In this persona, Archer is putting himself back in control. People with Borderline Personality feel powerless to influence their fate. They compensate for these feelings by omnipotent fantasies of unlimited power.

The millionaire author loved by a sympathetic public

Archer attends a prison religious service: 'We are all ready for the sermon and what a sermon it turns out to be.

'The chaplain opens the Bible: "The biggest bestseller of all time," he says, glancing in my direction and winking. His chosen theme is murder - "And it all began with Cain and Abel," he tells us.' (Kane and Able is the title of an Archer novel).

The diary is chocabloc with self-referential exercises in ego massage. In the newspaper serialisation of his diary I counted three occasions on which he supposedly meets men who tell him how much they love his books and that they have read them all. This is not always completely plausible.

An unnamed double murderer approaches him to say: 'I would like to say how much I enjoy your books. I've been in here for 11 years and I've read everything you've written'. I'm speechless. 'And by the way,' he adds, 'if you want that bitch of a secretary bumped off [Angela Peppiatt who gave evidence against him in his trial] I'll be happy to arrange it.'

One reason to doubt the veracity of this story is that Archer nearly always names prisoners whom he quotes, but not this time. There is more than a hint that Archer the manipulator is at work here, sending a vicious message - how would you feel if you were Angela Peppiatt reading this?

But Archer the fantasist is also involved, trying to feel he has a large adoring readership. Like all Borderline Personalities, he is a man with a massive feeling of insignificance and inferiority constantly finding ways to make himself feel special and superior. Hence his constant repetition of the 'fact' that he is receiving '100 letters a day' from members of the public supporting him.

The man who learns nothing from his experience

One of the strangest things about the diary is that there is not the smallest sign he feels he has done anything wrong. You might suppose the devout 'repentant sinner' - a role now played by Jonathan Aitken, Archer's equally impostorous old Tory mucker - would be a persona he would assume. But there is only a maudlin self-pity and it is all the fault of his devious, disloyal enemies.

When I interviewed him in 1987 I tried to find out if his failures had led to self-examination. His response was: 'You just carry on - that is what you do. You just carry on. I was a bloody fool.' But why? 'Because I was naive.' Why, Why? 'Because I am. Most enthusiasts are.' He was genuinely emotionally illiterate.

Interestingly, he admitted that Mary made no attempt to force him to question his personality, and they did not stop to analyse why he kept making such a mess of his life. She appears today to uphold his view that he is the victim of unfair treatment from the Prison Service and the courts. Certainly, this was his father's approach to his own many illegalities and I suspect his mother was equally prepared to turn a blind eye. Like the refusal of Manchester United's Alex Ferguson to admit any fault after the latest atrocity from his player Roy Keane, Mary seems morally blind to Archer's antisocial behaviour.

If she is no longer perfumed by moral fragrance, the same can be said of his near-neighbour John Major. It was always a mystery how the supposedly unimpeachable Major could be so close to such a manifest chancer but now we know they were both philanderers, perhaps sharing a tale or two of their sexual exploits over a beer. Perhaps, too, it was Jeffrey who, following his success in the Coghlan trial, suggested using a libel writ against the New Statesman to throw the press's scent off Major's affair with Currie.

After Major was booted out he used this metaphor to describe his position: 'When the curtain falls, it's time to get off the stage.' You could almost hear him talking to himself as a character out of a Trollope novel while he declared he was now going to the Oval cricket ground to watch the Test match. Like Archer, he was a self-invented confection, probably another 'as if' personality.

If only Archer had stuck to his true vocation - motivating small boys to get fit. Instead, his life has been a falsehood and the prison diary is an important document in only one respect. Whether we are talking about the people, like Thatcher, Major, Aitken or the Hamiltons, or about the political and corporate fiddles - from Lloyds to pensions to the robbing of the poor to give to the rich - its existential falsehoods embody an era of inauthentic fraudulence.

If only one could feel confident that that era has ended.

· Psychologist Oliver James's analysis of Jeffrey Archer is to be found in his new book 'They F*** You Up' (Bloomsbury, £16.99).

Borderline behaviour

There are nine traits that borderline personality disorder patients have in common. The presence of five or more may indicate BPD if they are long-standing, persistent, and extreme.

· Frantic efforts to avoid real or imagined abandonment

· Pattern of unstable and intense interpersonal relationships characterised by alternation between extremes of idealisation and devaluation

· Identity disturbance: markedly and persistently unstable self-image or sense of self

· Impulsivity in at least two areas that are potentially self-damaging (eg, spending, sex, substance abuse, reckless driving, binge eating)

· Recurrent suicidal behaviour, gestures, or threats, or self-mutilating behaviour

· Affective instability due to a marked reactivity of mood (eg, intense episodic dysphoria, irritability, or anxiety usually lasting a few hours)

· Chronic feelings of emptiness

· Inappropriate, intense anger or difficulty controlling anger (eg, frequent displays of temper, constant anger, recurrent physical fights)

· Transient, stress-related paranoid ideation or severe dissociative symptoms