LONDON • Amid olive trees and plenty of Abba tunes, the musical world of Mamma Mia took over a London theatre on Monday for the film sequel's world premiere, with Oscar winner Meryl Streep and pop diva Cher among the attendees.

Ten years after the movie version of the hit theatre musical, Mamma Mia! Here We Go Again sees old faces return and new ones join the Abba sing-along set on a picturesque Greek island.

The plot follows on from the first film, which grossed more than US$600 million at the box office, but, this time, has flashbacks explaining how Streep's character, Donna, arrived in Greece.

While fans have highly anticipated the sequel, Swedish band Abba's founding members Benny Andersson and Bjorn Ulvaeus said they were not so keen on the idea at first.

"We were kind of protective of the first one because we were very proud of it, it was very good and it became kind of a cult movie... and, we thought, what's the point of risking... taking away from that legacy, so we were reluctant," Ulvaeus told Reuters.

But the writers' idea of making the movie a sequel and prequel at the same time helped change their minds, he said.

"I laughed out loud many times when I read (the script's first draft). It was funny, it was moving, so we said go ahead, and here we are."

Chanting Waterloo, Super Trouper and Dancing Queen, fans cheered as Streep, Pierce Brosnan, Colin Firth, Amanda Seyfried and Christine Baranski - who starred in the 2008 film - arrived.

The sequel's cast additions include Lily James, who plays the younger Donna, and Cher, who portrays Donna's mother.

"I don't know what I was expecting, but I walked onto the set and I just thought, everyone's just having fun," Cher said.

Like the first film, the sequel has plenty of colourful and comic scenes. It also has touching moments, cast members said.

"It's a great time for this movie to be out in the world because we're all feeling a little down about the world right now," Baranski said.

Mamma Mia! the musical originated more than 20 years ago and has gone on to have productions around the world, with generations of fans still singing and dancing to Abba songs some 40 years after their release.

"It's so humbling and I'm grateful, but I cannot say I understand quite how that happened. It's kind of a miracle," Ulvaeus said of the band's success.

"Never in our wildest dreams did we think that these songs that we wrote would last for such a long time."

REUTERS