Paul McCartney has admitted that he still doesn't "know how to be a songwriter."

The former Beatle says with each album he has to start from scratch when it comes to penning lyrics.

"There's no point where you think 'OK, now I can do it', as it's a little more fluid than that," "You talk to other musicians and it's always the same.

You go into the studio thinking 'Oh, I know how to do this', but then you realize you're doing it all over again and starting from square one again.

You've never got it down. Music is fluid, and I like that.

I wouldn't like to be blasé and think 'I know how to do this.'"

McCartney released his last album, New, in 2013.