Ferguson has been at Man Utd for over 20 years

United were crowned champions after Chelsea drew at Arsenal and Ferguson, 65, said: "Why should I give up?

"I feel invigorated by the young players at the club and players like Ryan Giggs, Gary Neville, Paul Scholes turning out every week for me.

"I don't know how long I will last now but I am enjoying it."

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Ferguson, who has been at the Old Trafford helm for over 20 years, had a change of heart in 2002 after announcing his retirement.

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"It is easy to retire. It was a quick decision. I did it years ago and regretted it within days," he said.

Asked how the latest title triumph rates with the previous eight, Ferguson added: "All of them were good.

"Maybe the fact that for two years Chelsea dominated the Premier League and we had a big job to do to catch them makes this one special.

"The key was a good start to the season and we did that very well. It gave us momentum and from that moment on we did not lose it."

Ferguson had initially vowed to avoid title rivals Chelsea's crunch game against the Gunners but his curiosity eventually got the better of him and he watched the last 15 minutes of the 1-1 draw.

I will never be surprised what Sir Alex Ferguson can do because I know what he is like as a person and as a manager. Whoever writes him off he always proves them wrong - and he has done it again Former Man Utd midfielder David Beckham

He revealed: "I went to see my grandson play; they won their league and we won ours!

"I was twiddling my thumbs. I watched the last 15 minutes at the Emirates and was in agony. My heart was in my mouth.

"It was a great effort by Chelsea, we have got to give them great credit."

Meanwhile, former United midfielder David Beckham, who Ferguson sold to Real Madrid in 2003, heaped praise on his old manager.

The ex-England captain said: "I will never be surprised what Sir Alex Ferguson can do because I know what he is like as a person and as a manager. Whoever writes him off he always proves them wrong - and he has done it again.

"He knows how good a manager Chelsea's Jose Mourinho is, he knows how good Arsenal's Arsene Wenger and Liverpool's Rafa Benitez are and he respects them but as a manager you are not going to get many bigger or more successful managers than him.

"As a United fan I am really happy for the manager and for the players."

Midfielder Beckham, 32, who is set to leave Real for Major League Soccer side LA Galaxy at the end of the season, believes Ferguson will already be focusing on United's FA Cup final showdown against Chelsea on 19 May.

"The good thing about the manager at United is that is what he does - he makes you move on. As soon as you have won a medal he does not stop there, he makes you want more," said Beckham.

"That is what he put into me and that is what he puts into the rest of the young players.