The Beatles
File photo: The Beatles, clockwise from top-left, John Lennon, George Harrison, Paul McCartney and Ringo Starr, pose in a carriage window of train before they left Paddington Station in London, March 2, 1964. Image Credit: AP

London: The Beatles' latest release "Now And Then" on Friday became the legendary band's first UK number one single in 54 years, with Paul McCartney calling it "a very emotional moment."

Artificial intelligence helped isolate late member John Lennon's vocals from a tape he recorded in 1978, two years before he was murdered.

They were combined with old session tracks, including parts by late guitarist George Harrison, and new lines from remaining members McCartney and drummer Ringo Starr to "reunite" the band for a final time.

The Official Charts Company announced Friday that "Now and Then" had climbed to number one following its release last week, making it the band's first chart-topper since "The Ballad of John and Yoko" in 1969.

The Liverpool group now claims the record for the longest gap between number one hits, and also the longest time span between an artist's first and last chart-topper.

The Beatles' first number one single was "From Me to You" in 1963, more than 60 years ago, and they have 18 in total.

Fastest selling single of the year

"Now And Then" is the fastest selling single of the year so far and has accumulated the highest number of one-week physical sales in almost a decade.

Celebrating the news, McCartney, 81, told Official Charts: "It's mind boggling. It's blown my socks off. It's also a very emotional moment for me. I love it!"

Despite being highly anticipated, "Now and Then", which comes more than four decades after Lennon recorded it as a demo, received lukewarm reviews from music critics.

"'Now and Then' is not terrible... But ultimately, it's kind of mundane," wrote Geoff Edgers in the Washington Post.

The Times daily in the UK said the song showed AI at its best.

Parts of it also conjured up "that classic, bittersweet, Beatles-esque flavour", wrote reviewer Will Hodgkinson.

"Unfortunately, none of this can mask the fact that the Last Beatles Song is far from a lost masterpiece," he added.

But Martin Talbot, chief executive officer of the Official Charts Company, said the sales proved that "Beatlemania has returned".

"If there were ever any doubts that The Beatles are the greatest band of all time, they have surely consigned them to history this week," he added.

The demo tape was given to McCartney by Lennon's widow Yoko Ono in 1994.

Two other songs, "Free As A Bird" and "Real Love", were cleaned up by the producer Jeff Lynne, worked on by the other former Beatles, and released in 1995 and 1996.

An attempt was made to do the same with "Now And Then" but the project was abandoned due to the technical obstacles, unsurmountable at the time.

The two surviving Beatles finished "Now And Then" last year, including Harrison's electric and acoustic guitar parts recorded in 1995.