Benny and Björn attended the London première of Mamma Mia! The Party at the O2 in London and were interviewed on the blue carpet and, seen during the show at their tables.  Björn made a surprise appearance and speech during the performance wearing his tour costume from 1977, looking remarkably good - and also at the finale back in his blue suit.  Making his appearance in his 1977 tour outfit explained the make-up he was wearing on the blue carpet!

1. Celebrity Radio with Alex Bellfield
   Alex Bellfield interviewed Björn and Benny and then a host of UK celebrities: comedienne and writer of Mamma Mia! The Party  Sandi Toksvig with Mamma Mia! The Party   choreographer Stacey Haynes, Mamma Mia! The Party  producer Ingrid Sutej, comedian Noel Fielding, Mamma Mia! The Party , creator Calle Norlén, actress Harriet Thorpe, broadcaster Vanessa Feltz, actress Gaynor Faye, actress Nadia Sawalha, actors Ian Hillard and Mark Gattis, choreographer Craig Revel-Harwood, broadcaster Gloria Hunniford, champion swimmer Sharron Davies and choreographer Arlene Phillips.
    
2. Celebrity Radio with Alex Bellfield
   An overview of Mamma Mia! The Party première showing all aspects and including Björn and Benny in the audience, Björn's 1977 outfit appearance and speech at the end.
    
3. Celebrity Radio with Alex Bellfield
   Björn's speech at the end of the evening.  He brought Mamma Mia! The Party producer Ingrid Sutej onto the stage with him.
    
4. Stage Faves
   Perry O'Bree interviewed the attending celebrities and managed to get Benny and Björn in his sights as well. Benny seemed a bit bewildered by his method!  The celebrities interviewed were choreographer Arlene Phillips, champion swimmer Sharron Davies, comedienne and writer of Mamma Mia! The Party  Sandi Toksvig with Mamma Mia! The Party   choreographer Stacey Haynes, choreographer Craig Revel-Harwood, broadcaster Gloria Hunniford, actors Ian Hillard and Mark Gattis, actress Nadia Sawalha, actress Gaynor Faye, broadcaster Vanessa Feltz, actress Harriet Thorpe, comedian Noel Fielding, drag artist La Voix and Mamma Mia! The Party producer Ingrid Sutej.  After the show, he also interviewed some of the cast: Fed Zanni (plays Nikos), Steph Parry (plays Kate), Joanna Monro (plays Debbie the Chef), Julia Imbach (Konstantina) and AJ Bentley (Adam).
    
5. Mamma Mia! The Party
   Their own social media posted a couple of videos of the evening.  
   1. The first one was of Björn's appearance in his 1977 tour outfit from a distance.

   2. The second one contained a brief interview with Benny and Björn and footage of the various celebrities: Mamma Mia! The Party producer Ingrid Sutej, actors Ian Hillard and Mark Gattis, actress Gaynor Faye, comedienne and writer of Mamma Mia! The Party  Sandi Toksvig with Mamma Mia! The Party choreographer Stacey Haynes, actress Nadia Sawalha, broadcaster Gloria Hunniford, choreographer Craig Revel-Harwood, comedian Noel Fielding, Swedish Ambassador Torbjörn Sohlström.  Cast members were also interviewed: Fed Zanni (plays Nikos), Joanna Monro (plays Debbie the Chef), Julia Imbach (Konstantina) and AJ Bentley (Adam).

       

6. Associated Press
   Footage of Benny and Björn in the O2, an interview and an interview with Björn, presumably from earlier in the day where he says where the initial idea came from.  Plus footage of Björn in his 1977 tour outfit.
    
7. Nyhetsmorgon
   They broadcast Björn's speech in his 1977 tour costume.
    
8. Unknown source
   Two videos on Instagram, both of Björn's speech in his 1977 tour costume.

Daily Mail;

Thanks to Laszlo Arvai c/o ABBA Village (no longer online) and Jan Bach,
YouTube links c/o Celebrity Radio by Alex Belfield