Paul woke up one morning in his top floor bedroom at the Asher's home in Wimpole Street with the tune for 'Yesterday' in his head. There was a piano by the bed and he went straight to it and started playing. "It was just all there," he said. "A complete thing, I couldn't beleive it."

Although at that point it had no lyric, Paul was worried that the tune itself might have been unconsciously plagiarized, and that what had seemed like a flash of inspiration may only have been a surge of recollection. "For about a month, I went round to people in the music business and asked them wether they had ever heard it before," he said. "Eventually it became like handling something into the police. I thought that if no-one claimed it after a few weeks then I would have it."

He then came up with the provisional title 'Scrambled Eggs' and began singing 'Scrambled eggs, Oh you've got such lovely legs', simply to get a feel for the vocal. This was a common practice and sometimes gave rise to interesting lines that were kept in the final version. "We were shooting Help! in the studio for about four weeks," remembers Dick Lester. "At some time during that period, we had a piano on one of the stages and he was playing this 'Scrambled Eggs' all the time. It got to the point where I said to him, 'If you play that bloody song any longer I'll have the piano taken off stage. Either finish it or give it up!'"

Paul must have conceived the tune early in 1965, but it wasn't until June when he took a brief holiday in Portugal at the villa of Shadows' guitarist Bruce Welch that he'd completed the lyric. He then hit on the idea of using a one word title - 'Yesterday'.

"I was packing to leave and Paul asked me if I had a guitar," says Welch. "He'd apparently been working on the lyrics as he drove to Albufeira form the airport at Lisbon. He borrowed my guitar and started playing the song we all now know as 'Yesterday'."

Two days after returning from Portugal, Paul recorded it at Abbey Road. The song startled pop fans at the time because it featured a string quartet with Paul as the only Beatle on the session. In America it became a single and reached the Number 1 spot but, in Britain, it was never released as either an A or a B side during the group's carrer. It rapidly became a pop standard, covered by everyone from Frank Sinatra to Marianne Faithfull. Nowadays, some 30 years on, it is still one of the most played tracks on the radio.

Although John claimed that he never wished that he had written it, he did admit that it was a "beautiful" song with "good" lyrics but argued that the lyrics were never resolved. However, others have felt that its strenght lies in its vagueness. All the listener needs to know is that it's about someone wanting to turn back the clock, to retreat to a time before a trafic event. The application is universal.

There has been speculation that in Paul's case the tragedy referred to was the death of his mother and the regret was over his inability to express his grief at the time.