We knew this day would have to come

And so it has finally happened: a fixture as seemingly irreplaceable, as immovable, and as unequalled as Sir Alex Ferguson has given his notice.

For months he's blown smoke on ideas of retirement. Just four days ago, in his programme notes for the Chelsea game, Fergie dismissed the idea of going anywhere, anytime soon, although he did seed a clue or two:

"This team of champions is not going away - we are here for the long ride. We will get better and if we apply ourselves in our normal fashion I see our 20th league title as nothing but the start of another decade of success."

But he added, crucially: "Whether I will be here to oversee another decade of success remains to be seen, but I certainly don't have any plans at the moment to walk away from what I believe will be something special and worth being around to see."

Walk away. Not walk upstairs, which is what he will do in a new, post-managerial role as a member of the club board. “The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time," Fergie declared in the club's official press release.

"It was important to me to leave an organisation in the strongest possible shape and I believe I have done so," he added. "The quality of this league winning squad, and the balance of ages within it, bodes well for continued success at the highest level whilst the structure of the youth set-up will ensure that the long-term future of the club remains a bright one."

Just how comfortable SAF will be up there in the Old Trafford director's box also remains to be seen. Not having him sat in the home dugout, chewing like a somewhat twitchy, ruddy-faced camel, will be odd enough for us, let alone for the irascible Scot himself. His new, lofty eyrie will certainly not be the environment to start waving his watch at refs or administering the Govan hairdryer to players or officials.

There's no point mincing words about Ferguson: he has, at times, been an unbearable bully. To his players and even players of other teams; to managers he doesn't like or to those who commit offence to managers he does; to journalists who've dared cross him and, of course, to officials and the authorities with the temerity to police him.

One can't deny that the bullying and discipline has, like that of a drill sergeant, produced results. Likewise The Sun newspaper was at its sharpest, its funniest, its most relevant and most read when under the shouty editorship of Kelvin Mackenzie (an under-estimatedly clever newspaper editor, not that you could mention such an opinion anywhere on Merseyside). Fergie may not have produced sensationalist newspapers, but in his application of the same tough love he produced two sensational generations of footballers.

This in-your-face swagger has also made Manchester United the club to envy and admire in equal measure. The United chequebook has lavished money on apparently untouchable signings like Paul Ince, Steve Bruce, Roy Keane, Eric Cantona, Ruud van Nistelrooy, Cristiano Ronaldo, Rio Ferdinand, Wayne Rooney - all for record amounts to leave us grinding our teeth (complain as you might about the Russian and Middle Eastern money sloshing about elsewhere, Manchester United set the bar high for eye-watering acquisitions).

And here is where we reluctantly, perhaps, cross the red line with Sir Alex. For all his bullying, for all his arrogance, for all the disingenuity, you have to admire him. He is retiring at the end of a staggering 27 years in charge of Manchester United. Compare that with Blackburn Rovers and Nottingham Forest who've managed to have four managers each in just this season alone. More importantly, compare Ferguson's record with that of the Manchester United's peer group: in the time Ferguson has been in charge at Old Trafford, Real Madrid have had 24 managers, Chelsea have had 18, AC Milan have had 13 and Inter Milan 19, and Manchester City, Juventus and Bayern Munich 13 each.

Manchester United's consistent success over the last three decades isn't just down to Ferguson, of course. He has been the integral element of a perfect storm that brought him together with Premier League money and the club's scale to develop young talent that have been blended perfectly with the acquired.

Those around the club have simply lacked all or some of these elements: Arsenal has had the manager, some of the money and some of the players, but the inability to maintain the investment. Manchester City and Chelsea have enjoyed the money via arriviste proprietorship, brought in the players as a result, but have yet to display anywhere near the consistency.

In Chelsea's case, in particular, the continuous managerial upheaval sets them apart from their great northern rival. It's interesting to note that in December 1989, Manchester United were hovering just outside the relegation zone of the old First Division. In today's terms, with the sort of proprietors that exist in the game, Ferguson could have easily found himself out of the door. United - to it's genuine credit - persevered. The club had the vision to recognise they were building something. And so they have continued in the same vein. Big names have come, big names have gone, youngsters have come through, and the club has successfully, and usually somewhat subtly, reinvented itself under Ferguson.

Manchester United haven't always had it all their own way under Sir Alex Ferguson: when Jose Mourinho's Chelsea took the Premier League title off them twice in 2005 and 2006 the chatter began, then, that the end of the Scot's tenure at Old Trafford was in sight. Now it is. The club is as strong as it ever has been. The next manager - be it a Moyes or Mourinho - will have large shoes to fill...and a large mountain of expended chewing gum to sit in front of.