Sir Paul McCartney writes all his songs by instinct.

The former Beatle and solo artist -responsible for some of the most enduring pop songs to date including 'Yesterday', 'Hey Jude' and 'Eleanor Rigby' - admits that when it comes to songwriting he does it without thinking about the process, and never analyses his work.

He said: "I'm still intoxicated by the fact I can do it. If I were to try and answer how I do it, I couldn't.

"I saw a guy on TV dissecting 'Penny Lane'. He said, 'McCartney starts off in this key and then he modulates down to sing higher'. I'm going, 'did I? Brilliant, well done, lad!' It's all instinct. I just sort of do it."

Paul, 67, also said that while he's enjoyed a career spanning over 40 years he still has a hunger to keep furthering himself - and that over time perspective changes his views of his earlier work.

He added: "Most artists I know feel like they have something to prove. That's what keeps you going, that sense you can do it better. I mean, I remember not really liking the vocal on 'Eleanor Rigby', thinking I hadn't nailed it.

"I listen to it now - and it's very good. It's a bit annoying when you do 'Eleanor Rigby' and you're not happy with it."