The 69-year-old musician, who used to hit the bottle at his hideaway on the Mull of Kintyre, says he was so drunk that he was unable to write songs.
"I overdid it, basically. I'd drink whisky, of which there was a large supply in Scotland. What happened was The Beatles, towards the end, was very constricting. "You were in a corporate world suddenly. It's not what you get into music for, but it's there.
It got very heavy, so me and Linda (wife) escaped with the kids, but the business hassles were still there. "So I think I was just trying to escape in my own mind.
I had the freedom to have just have a drink whenever I fancied it. I'd go into the studio, maybe have another drink and so on. I got to a point where Linda had to say 'Look, you should cool it'," he said.