I'd lost one of the greatest jobs in the world and suddenly there I was, feeling totally redundant

Sir Paul McCartney

The two-hour film, Wingspan, which also features unseen his home-movies of his late wife Linda, will be broadcast on Channel 4 on 12 May.

"When The Beatles finished at the end of the 60s it was such a shock to my system. Besides being out of work, to my mind I'd lost one of the greatest jobs in the world and suddenly there I was, feeling totally redundant," said Sir Paul.

"I started staying up all night and then staying in bed all day - there didn't seem to be any point to getting out of bed.

"I stopped shaving. I started drinking Scotch and I just sort of went a little crazy for a few weeks. Looking back on it now, I guess I nearly had a breakdown."

Sanctuary

Wingspan reveals how the McCartneys sought sanctuary at High Park Farm near Campbeltown on Kintyre.

Sir Paul says Linda talked him through his despair

"We went up to Scotland. I just had to get out of London and get in the mist and the mountains - just to try walk around and get some air and get away from this trauma."

Wingspan tells the inside story of how the McCartneys struggled to raise a young family while trying to follow The Beatles with their seventies rock band Wings.

The film was one Linda's projects in the last year of her life. She died from breast cancer in 1998.

"I had to decide whether I wanted to carry on in music or to give up music and try another job," said Sir Paul.

Hard act

"I realised that I just loved music too much to stop doing it. But then I realised that if I carried on I would have to try to follow The Beatles - and that was the hardest act to follow."

"At the depths of my despair, Linda would be there just to say 'It's OK, you're really alright'... She'd kind of talk me through it. She'd get me to go for a walk with her to clear my head or go riding the horses."

It was at Kintyre that Sir Paul decided to form Wings.

Sir Paul says that he wrote his biggest selling-single Mull of Kintyre as "a Scottish waltz" to say thank you to Scotland.

"I was very surprised how big it became," he said.

Wingspan, the 40-track album of Wings' greatest songs, will be released on 7 May.