Per the Cleveland Leader:
The Beatles, 12 years after releasing Free as a Bird and Real Love from the John Lennon vault, are recording a new song by the late Beatle for one last final hurrah. The song is called 'Now and Then'. McCartney, working with a finished Lennon chorus, has written verses to go along with Lennon's unfinished song.Here's more detail from an article in Yahoo News:
The song is set for release sometime later this year but no firm date has been given. The late George Harrison had blocked the track from release as he was not as high on the song as McCartney. Some Beatles insiders say that the is it is McCartney's goal to release one more song that will be forever ever remembered and cementing the Fab Four's legacy even further.
The surviving members of the Beatles are set to release a never-before-heard new single.
The track, called Now and Then, is based on a John Lennon recording, given to Sir Paul McCartney by Lennon's widow Yoko Ono in 1994 as part of their Anthology project.
According to friends this may now be the "one last great song" that McCartney has been waiting for since he recommenced touring and working in 1989.
"Paul was asked in the early Nineties when he started touring again, why he was doing it. They said that he was rich, he didn't need this. But Paul said that he felt he had one great song left in him. He's always been the most uncannily intuitive person and it looks like that song has finally arrived," the Daily Express quoted ELO musician Jeff Lynne, who produced the sessions, as saying.
Archive tracks from George Harrison will also be merged with the new song, along with vocals from McCartney and drumming from Ringo Starr.[...]
Lynne also said that the best thing about the song was that it brought back a lot of memories.
"The best thing about it all was to work with John again. Hearing him in the headphones, it was like he was in the next room. It's like an impossible dream," he said.
According to sources, McCartney has reverted to the drawing board and will conclude the song the way he and John always worked, making it a suitable Lennon-McCartney masterpiece.