The legend, 70 this month, confessed his whisky drinking got out of hand when he went to his Mull of Kintyre hideaway.
It was so bad in 1970 it worried his first wife Linda and led to him being unable to write songs.
Sir Paul said: "The Beatles got very heavy, so me and Linda escaped with the kids, but the business hassles were still there.
"I over did it, basically. I got to a point where Linda had to say 'look, you should cool it'."
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