Sir Paul McCartney wrote new song Alligator while sipping green tea and waiting to call his wife Nancy Shevell in New York.

The former Beatle had just dropped his daughter Beatrice off at school in England and was back home trying to pass the time before his wake-up call to his missus when he started musing on the guitar.

He says, "I knew that in about three hours time... after I started I would be gonna (sic) ring Nancy, who was in New York... so this gave me a motivation to write something and ring her and say, 'Mornin' baby, wanna hear a song?'"