Sir Paul McCartney believes song writing acts as a psychiatrist.

The 71-year-old icon admits some of his most successful tracks, such as 'Yesterday' and 'Got To Get You Into My Life', have been penned during particularly emotional times, as writing lyrics allows him to release the ''demon'' inside him.

He said: ''I think it's good when you're in a dark period, the good is [the song's] your psychiatrist, it's your therapy, and you know we have many tales - anyone who writes has.

''Going away when you're really upset about something and putting in your song - you come out of that cupboard, toilet or basement and go, 'I really feel better'. You've actually exorcised the demon. So it's one of the great joys of song writing.''

The former The Beatles musician says he lives for the rush he gets after he's written a good song, because it allows him to deal with negative emotions and see things in a different light.

He explained to Mojo magazine: ''It's like writing your dream out or something, and it's a physical effect where you come back out and you've created magic again, pulling the rabbit out of the hat 'Where did that come from?' Wahey! It's a great feeling.''