They have turned down a billion-dollar offer to re-form for a one-off concert. But last week the creators of Waterloo, SOS and, most importantly, Mamma Mia, were briefly reunited on a stage as they attended the opening of Mamma Mia! The Party - a themed restaurant inspired by their ‘jukebox musical’ and movie.

Questioned by reporters, keyboard player Benny Andersson maintained that he didn’t think the four of them would ever get back together as performers. Guitarist, and Andersson’s co-writer on ABBA’s almost endless catalogue of hit records, Björn Ulvaeus agreed. “We are here to party,” he said.

The quartet, probably the biggest pop act in history after The Beatles, hadn’t been pictured together since 2008. At the restaurant opening on Friday, they arrived in separate cars and were careful not to be photographed together on the red carpet, although they assembled briefly on the stage.

Mamma Mia! The Party is inspired by the Greek taverna in the Andersson / Ulvaeus musical. It promises an immersive ABBA-themed experience together with a tasty three course Mediterranean buffet.

The entire affair is housed inside Stockholm’s already well-established Tyrol restaurant. Despite the Scandinavian climate, the temperature at Nikos Taverna is, the website assures us, always set on Greek high summer, regardless of season.

Björn is the principal driver behind the restaurant venture but former bandmates Benny Andersson, Agnetha Fältskog and Anni-Frid Lyngstad were all on hand to help him launch it.

The group is thought to have sold in excess of 380 million albums and singles worldwide although precise figures are not available and sales could be as high as 500 million records.

Their final public appearance was for Noel Edmonds's The Late, Late Breakfast Show, on December 11, 1982.

The group’s songs gained an extra lease of life through the Mamma Mia! musical, which weaves over 20 of their hits into a story set in a Greek taverna. The show has been a phenomenal success. On any given day, there are at least seven performances of Mamma Mia! around the globe and it’s one of the longest-running shows ever on Broadway.

Whether that success will translate into the world of ouzo and stuffed vine leaves remains to be seen, but for now the restaurant’s success looks more certain than a full ABBA reunion.