If you want to know what makes Alex Ferguson tick, you have to get up early. He might not like to hear it ("never, ever mention my name in the same sentence as that woman," this lifelong Labour supporter once snapped), but one trait he shares with Lady Thatcher is an apparent ability to go on and on without needing to recharge the battery.

An average working day, which will end pouring over videos of opponents at one in the morning, will have begun 18 hours earlier. His is invariably the first expensive car to arrive at United's training ground, the Cliff, arriving usually before seven. Exhibiting what another friend calls "a psychopathic energy", he will have already accomplished three or four tasks before Dwight Yorke's Ferrari, or David Beckham's Bentley, comes purring in.

Early in the morning, in charge, in his domain, Ferguson is completely different from the edgy figure we have grown used to on our television screens, patrolling the touchline stop-watch in hand, volcanic temper barely in check. Here he is relaxed, avuncular, joking with groundsmen and cleaners, belting out snatches of light opera in a more than passable baritone. Here he is in control - and there's nothing he likes more than control.

Any visitor to the Cliff is left in no doubt from the moment they arrive who's in charge. "Strictly Private" reads the notice on the door of the changing-room building. "Absolutely no admission without the manager's permission." He likes to know everything: from who is conducting an interview with one of his players, to the collar design for the latest replica kit to emerge from the United mega-store (this month's is the 48th), to how the under-17 team fared in their latest match. And it was Ferguson who went to Manchester's Bootle Street police station last Tuesday to get Roy Keane, the United captain, freed when he was held overnight after an incident in a bar, adding another page to the legend of Man U - the Red Devils.

Even now, in his 13th year at Old Trafford, Ferguson will be the representative of Manchester United who appears at the doorstep of a promising teenage player to persuade his parents that he really should sign up for the club. Ryan Giggs's mother remembers it was Ferguson's arrival at her house that made her think that, even though other clubs had made more lavish promises, this was an employer who would care for her boy.

The former United hero, Norman Whiteside, now makes a handy living out of an after-dinner speech centring on the occasion he was hustled out of the back door of a pub by the landlord after Ferguson was spotted marching in through the front, an A-Z of Manchester in his hand with which he had plotted the wayward Irishman's drinking spree. Those who have been at the wrong end of a bollocking (much of the British football media) frequently use words like "paranoia" and "siege mentality".

But importantly, among his players, there is a fearful respect for his Stalinistic omnipotence. "Listen, at that club you have sleepless nights if you play badly in the reserves," says Les Sealey, United's former goalkeeper.

"Honest, there's always someone watching you. And if you slack, word will get back. To him." This will be music to Ferguson's ears. "Control is everything in management," he says. Journalists moan constantly about the ridiculousness of a multi-million pound corporation failing to employ a press officer and instead requiring every request for a player interview, every query about minor details of injury and fitness to be channelled through the manager's office. "Unless you have control," Ferguson says, "you can't have a vision, targets, dreams. In football life, the only thing that gives you control is time and the only thing that buys you time is success. Not every manager has time, unfortunately. Some of them opportunity."

"He sees football as a cause," says Mark McGhee, who played under Ferguson at Aberdeen. "A cause to which he expects you to give 100 per cent. Everything else is secondary. And I mean everything else. He only wants people around him who are prepared to accept the challenge, as he calls it. To take on the cause - his cause: to prove everybody wrong."

This, according to McGhee, is a product of his upbringing. Ferguson is a son of Protestant Glasgow, who, after five years in the shipyards, achieved the ultimate expression of his culture by playing centre-forward for Rangers, the team regarded as representing - at least unofficially - sectarian Orangemen. He wasn't the greatest of players, but he was fiery, determined, constantly anxious to prove his worth, qualities apparently handed out with the birth certificate where he came from.

Yet he has not taken from his cultural heritage any of the baggage of loyalism. He has no problems managing a traditionally Catholic club like United, makes no judgment about a player's background, creed or race beyond whether they can play. The political world-view he drew from his upbringing was more class-based, more unions than unionism; at 19 he led an unofficial walk-out in Govan shipyard over a pay dispute.

He has always made it clear he is proud of being Scottish, working-class and Labour supporting; he has never gone on record about his religious affiliations. His personal attitudes reflect his origins. Intensely loyal to those few he trusts, he regards family ties as the most vital (his brother Martin works for him as a scout and a spy).

Nonetheless, he admits he has always delegated all domestic duties to his wife Cathy. He says it was she who brought up their three sons (Darren, who has had a reasonable career as a player with United and then Wolverhampton Wanderers; Mark, a television producer; and Jason, who works in the City) and occasionally wonders if he hasn't seen more of his grandchildren as they grow up than he did of his own boys.

More pertinently, though, the sports writer Hugh McIlvanney believes Ferguson shares a common bond with Bill Shankly, Jock Stein and Matt Busby, the great triumvirate of Scottish football managers. Like them, McIlvanney reckons, he learnt from working in unforgiving circumstances how to assess the qualities of the men around him. His seemingly natural ability to understand how an individual is best motivated, which he has put to such effect in football, was honed by the world of real work.

Yet when he came south to England, his great motivational talent - which had served him so well at Aberdeen - seemed no longer appropriate. Many of the players he inherited on arrival in Manchester, used to his cavalier predecessor Ron Atkinson, found it hard to respond to this ranting Roundhead in their midst. When he is not in control, Ferguson suffers. And in the autumn of 1989 he was suffering as his team sank towards the relegation zone.

It is hard to imagine now - contemplating the full-house of trophies there to be won in one season, with the biggest contract in managerial history sitting in his desk drawer - that almost exactly a decade ago, the bookmakers had closed the betting on Ferguson being sacked by United. The former East Stirling, St Mirren and Aberdeen manager was sinking in his new job. He had achieved unparalleled success north of the border, taking Aberdeen to the kind of sustained success (including a triumph in the European Cup Winners Cup) unmatched before or since outside the dominant hegemony of the two big Glasgow clubs, Rangers and Celtic. Yet at first on his arrival in Manchester his methods appeared too parochial.

"He was in awe of the place when he first came down, no question," says Norman Whiteside. "He used to come up to us in training and say, `big place this, big place'." It was understandable why any new United manager should have been intimidated back then. The scale of the job was enormous: the most widely supported club in the land, the most financially muscular, hadn't won the league for two decades. But turning round a woefully under-achieving operation, a place infected with an over-inflated sense of its value, had proved too much for several of his predecessors. They had wilted in the shadow of the man who had created the United myth, Sir Matt Busby.

Looking back now, Ferguson, who loves his football history, says that was the very reason he took the job.

"The tradition, the history, the romance of the place appealed," he says. "People said it was an impossible job, that Matt Busby was an impossible act to follow, I loved that challenge. I thought it was great he was still around the place. I thought it was a bonus, whereas a lot of people were intimidated by it." At the time, though, it seemed from the outside that Ferguson was destined to be another casualty of the Busby legacy. His team was faltering, his purchases seemed panicked and short-term, the crowd had turned against him. The mood was summed up by a flag unfurled in Old Trafford during the match which marked his third anniversary in charge: "Three years of excuses," it read. "Ta-ra Fergie."

The Ferguson of the autumn of 1989 seemed a man out of his depth. His one managerial tactic appeared to be yelling, his one motivational idea fear. Such was the scale of his fury that the dressing room was a dangerous place to be. On one occasion, he hurled the contents of the kit-skip around the room and a jockstrap landed on the head of one player, who sat petrified until he got a further bollocking for daring to sit there during a bollocking with an athletic support on his head.

Mark Hughes, who won half-a-dozen medals under Ferguson in the 1990s, says: "It used to scare the living daylights out of us, but we realised it was only because of that tremendous will to win." What Ferguson had attempted to do at Old Trafford was turn the place round as he had at Aberdeen. Up there during the 1980s, he had created a vibrant, trophy-accumulating machine by painting the dominant forces of Scottish football - Rangers and Celtic - as the enemy and Aberdeen as the gallant outsiders.

At United, it was a piece of luck that began the recovery: an FA cup-tie was won by a goal from a young reserve, Mark Robbins, only playing because of an injury crisis. United went on to win the cup that year, and Ferguson had bought himself the time he needed to create the club in his own image.

Fortunately for him, the United board had more foresight than the fans. "During that time we never, ever discussed Alex Ferguson's position," says Sir Bobby Charlton, a club director. "Because we knew what he was doing was right." Out went the old players he called "the swaggering socialites" and in came the committed, many of them youngsters growing up to his blueprint: hard-working, focused, disciplined. What they found, as well as the fearsome temper, was a manager prepared to reward those who took up the cause. "He put pressure on you to perform all the time and he expected you to have the mental strength to withstand it," says Mark McGhee. "If you repaid him, he was incredibly loyal to you. But if you didn't, he wasn't slow to tell you. He was very honest."

It seems a trivial thing, but his players responded to the way in which he would never criticise them in public. More than that, he would do his best to deflect attention from their misdemeanours by what he called diversionary tactics. Watch him after one of his players has misbehaved, and he will usually offer some outlandish comment - about the referee, the opposition, Radio 5 Live's commentator, anything - designed to steal the next morning's headlines away from their behaviour. He will then go back to the dressing room and administer a medieval bollocking to the offender.

"I will never start slagging my players off in public," he says. "When a manager makes a public criticism, he's affecting the emotional stability of a player and that cannot be a very professional thing to do.