The song was written by Lennon and has him singing and playing on it. Using digital technology, the three surviving Beatles were able to add their contribution to the tape to make the first 'new' Beatles song since 1969.
But is there a market for a new Beatles single? Music industry sources, including longtime Beatles fans, agree that there may not be. Traditional Beatles fans are too old to buy singles, and teenagers will not automatically buy a record just because it has the Beatles' name on it.
There is also unease about using a John Lennon tape and adding his voice to those of Paul McCartney, George Harrison and Ringo Starr - perhaps a psychological need for McCartney to be in harmony with his old partner.
McCartney, Harrison and Starr have met secretly to record the song. They used a demo tape of Lennon singing the number, making it the first time all four Beatles have combined on a song since the Abbey Road LP was made in 1969.
The song is part of a soundtrack to The Beatles Anthology, a 10-hour series about the group, to be shown on television next year. The soundtrack will also feature some unreleased early Beatles material.
The last Beatles single was Let It Be, released in the spring of 1970; but it was recorded nearly 18 months earlier, and by the time it was released the Beatles had split up.
While the music industry has no doubt of huge sales for the boxed set that will accompany the television series, some feel the surviving Beatles should not issue the new song as a single.
Paul Du Noyer, editor of the rock magazine Mojo, was doubtful about the song's chances of success as a single, and also about using Lennon's voice.
He said: 'On the face of it, the exercise looks unpromising. Using a tape of John doesn't seem the most organic method of producing music. And you have to ask why he didn't release it himself while he was alive.
''But I'm sure Paul misses John's creative input terribly. John was a very harsh critic and he was always there to curb McCartney's syrupy excesses.'
McCartney, who is in America, told journalists at Heathrow Airport before he left: 'We are keeping the title and all that very quiet for now because we've got to sit on it for a year until it is released. But it's a pretty good little song.'
Recording with his late partner was 'sort of creepy at first', he said, 'but we took the attitude that he'd just sent us a cassette and said, 'I'm going on holiday, finish it off. I trust you, do whatever you want to do.' And that's what we did. We had a great time, a great week in the studio, and it worked out great.'
Lennon's widow, Yoko Ono, gave the project her blessing.
The 'new' Beatles song is not the first time a record has used a bizarre mix of living and dead artists. Two years ago Natalie Cole sang a 'duet' with her dead father, Nat King Cole, on her and formerly his hit single Unforgettable.
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