Video report by correspondent Victoria Grimes.
The Beatles have released their final single - featuring 50-year-old vocals from John Lennon.
It has been branded a “qualified success” and a "toast to days gone by" by music critics.
In his review, The Guardian music critic Alexis Petridis awarded the song four stars out of five and called it a “qualified success”.
He wrote: “Advances in technology have solved the problems with Lennon’s vocals….
“The other potential vocal problem – at 80, McCartney’s voice has aged considerably since the remaining Beatles last reconvened – is solved by keeping him low in the mix: you feel his presence rather than notice it directly.”
Take a listen to The Beatles 'final every single' Now And Then.
But music critic for The Telegraph, Neil McCormick had a different take.
Offering the song three out of five stars, the critic said that “the McCartney-led chorus arrives as an anticlimactic plod,” adding that “the chords aren’t interesting and harmonies pasted in from old Beatle recordings”.
In spite of this, McCormick said that he is “glad it (the song) exists” and described it as a “toast to days gone by.”
The track, sourced from a Lennon demo, used technology to extricate and isolate his voice.
The world-famous band released the song as a double A-side with the band’s 1962 debut single Love Me Do, and cover art by US artist Ed Ruscha.
It was recorded by the singer in the late 1970s at his home in New York’s Dakota Building.
After his death in 1980 aged 40, Lennon’s wife Yoko Ono gave the recording to the remaining Beatles in 1994 along with Free As A Bird and Real Love, which were released by the band in the same decade.
During this period, Harrison, Sir Paul and Sir Ringo recorded new parts and completed a rough mix for Now And Then with producer and musician Jeff Lynne.
However, the band did not release the song, citing issues separating Lennon’s vocals and the piano in a clear mix due to limited technology at the time.
But in 2021, new artificial intelligence audio restoration technology allowed Peter Jackson and a team to isolate vocals and music, creating a new mix of the Revolver album, sourced directly from the four-track master tapes.
Jackson and his sound team, led by Emile de la Rey, have now done this for Now And Then, which helped separate the vocal from the piano.
Sir Paul and Sir Ringo finished the song in 2022, including Harrison’s electric and acoustic guitar recorded in 1995.
Sir Ringo’s drum part was added alongside bass, guitar, piano and a slide guitar solo by Sir Paul, inspired by Harrison, as the surviving Beatles also put on their backing vocals to the chorus.
Recorded at Capitol Studios in Los Angeles, Sir Paul oversaw the track as more backing vocals were added from the original recordings of Here, There And Everywhere, Eleanor Rigby and Because.
The finished track was produced by Sir Paul and Giles Martin – who both wrote the string arrangement alongside Ben Foster – and mixed by Spike Stent.
Sean Ono Lennon, son of Lennon and Ono, said: “It was incredibly touching to hear them working together after all the years that dad had been gone.
“It’s the last song my dad, Paul, George and Ringo got to make together. It’s like a time capsule and all feels very meant to be.”