Sir Paul McCartney has spoken of his inspiration for the Beatles’ hit Lady Madonna – a woman breastfeeding her child.

The 1968 track reached the top of the charts and is one of the most famous releases from the Fab Four.

Sir Paul said he was inspired to write the song after seeing an image of a woman in National Geographic magazine in the 1960s.

National Geographic’s January 1965 issue published a photograph entitled Mountain Madonna, of a woman whose way of life was threatened, with one child at her breast and another laughing up at her.

Wirral Globe:

Mountain Madonna picture in National Geographic (Howard Sochurek/National Geographic)

“She looked very proud and she had a baby … And I saw that as a kind of Madonna thing, mother and child,” Sir Paul said.

“Sometimes you see pictures of mothers and you go ‘She’s a good mother’. You could just tell there’s a bond and it just affected me, that photo. So I was inspired to write Lady Madonna, my song, from that photo.”

Sir Paul also spoke of not getting tired after a three-hour show, despite performing at the age of 75.

“I think I feel very healthy and I do shows three hours long and I don’t feel knackered at the end of it. I still feel strong,” he said.

The singer was speaking to National Geographic editor-in-chief Susan Goldberg about his Meat Free Monday campaign and new documentary short.

The film features daughters Mary and Stella McCartney, as well as actors Emma Stone and Woody Harrelson.

The vegetarian, discussing the effect of livestock agriculture on climate change, said: “We’re on this incredible planet and there doesn’t appear to be another one within sight.”

:: Documentary film One Day A Week is released on Friday on YouTube.