Sir Paul McCartney "immerses" himself in song writing.

The Beatles legend's debut ballet 'Ocean's Kingdom' premiered in New York this week and while it was a new venture for the 69-year-old star, the musician enjoyed writing for the project just as much as making his usual records.

He said: "I enjoy writing music full stop, so whether it's an orchestra or rock, I immerse myself in it."

Paul admits he sometimes found it a "challenge" writing such emotional pieces of music for the ballet but he is pleased he agreed to the project.

He added: "What was interesting was writing music that meant something expressively, rather than just writing a song.

"Trying to write something that expressed an emotion was very interesting, so you have fear, love, anger, sadness to play with and I found that very interesting and challenging, but great. I'm really glad I accepted."

Paul's fashion designer daughter Stella has created the costumes for the production, and the rocker loved working closely with her.

He said: "It's been great working together. It's been very special."