Since [The Beatles’] split, you can see how important it was when the four of them were together. I met Paul McCartney in New York recently and he was talking to me about the album he was doing - the second one, Ram. He said you can’t believe how hard it is when you’ve worked with people for that amount of time - the same four people working together - and you come up with a song. And…everybody just fits their bit and it’s there. I know exactly what Paul means, because it’s like that with [Led Zeppelin].