Buona Sera, Mrs Campbell is a little-known American film released in 1969. A comedy-of-manners starring Telly Savalas, it concerns a woman in wartime Italy who, driven by dire circumstances into prostitution, deceives three of her American GI clients into financially supporting her daughter by telling each of them that he is the girl's father.

Twenty years later, the men return to her village for a reunion with a daughter each believes is his and our industrious heroine resorts to all manner of hilarious tactics to ensure that her secret does not come undone. The film died at the box office -- but it would live on in another guise more than 30 years later.

In 1997, the movie would prove a key inspiration for jobbing British playwright Catherine Johnson who had been approached by veteran musical impresario Judy Cramer to write a musical based on the songs of ABBA. Mamma Mia! was born.

In Johnson's version, the story concerns a young Greek bride-to-be whose quest to discover the identity of her real father brings three men from her mother's past back to the island they last visited 20 years ago. It features 22 different songs from the Swedish pop icons' vast repertoire.

The musical has become a bona fide global phenomenon. Since its debut in 1999, 30m people have seen it and sung along to ABBA's songs. It has made $2bn at the box office, and played in 160 cities around the world, including a hugely successful run at Dublin's Point Depot. To put its popularity in context, the musical pulls in almost €5m per week.

Quite simply, it's one of the most successful musicals of all time and has helped make the songs' principal songwriters Bjorn Ulvaeus (the lyrics man) and Benny Andersson (responsible for the tunes) among the wealthiest people in entertainment. They were already well into the black, having sold some 350m ABBA albums before Mamma Mia! proved to be the phenomenal money spinner it became.

Now their coffers are set to be lined even further with the release of the movie version of the play which features an all-star cast including Meryl Streep, Pierce Brosnan, Colin Firth and Julie Walters.

The world premiere at London last week had oodles of old-style glamour and it is thought that the film will be among the most lucrative of the year at the box office. Everything connected with the ABBA name, seems to turn to gold.

Despite this, the best selling act of the 1970s suffered a lean period after the group split in 1983. For the best part of 10 years, the foursome -- who took their name from the first letter of each member's name, Agnetha (Faltskog), Benny, Bjorn and Anni-Frida (aka Frida) -- were dismissed as an embarrassing remnant of the previous decade.

The rehabilitation would commence in the early 1990s, thanks to the release of the ABBA Gold compilation, the ABBA-referencing Australian movie Muriel's Wedding and as a result of such disparate bands as U2, the Sex Pistols and, notably, Erasure bigging up their music. They are still one of the best-selling acts in the world, shifting 3m back catalogue albums every year.

Since their split, Bjorn has said they have resisted regular offers of "more money than you'd believe" to reform the group, including a rumoured $1bn offer in 2000. "Our legacy is best served by not reforming," is his standard response.

Since the band parted company due to irreconcilable differences -- the marriages of Bjorn and Agnetha and Benny and Frida having ended some years before -- each of the four members have had very different experiences.

Benny and Bjorn tried their hand at the world of musicals early on, but their collaboration with Tim Rice on Chess got a lukewarm critical reception and wasn't the global smash its creators had imagined. In the 15 years between that failure and the early development of Mamma Mia! the pair stayed largely out of the limelight.

The stories of their former wives could hardly be more different. Frida, two divorces down, is now happily married to Prince Ruzzo Reuss von Plauen. A strict vegetarian, she was back in the Swedish charts at the end of the 1990s with her Wonderful World duet with Roxette's Marie. She has a financial involvement with Mamma Mia! and frequently attends the shows.

As for Agnetha, once voted owner of The Most Beautiful Bum In The World, her marriage to a surgeon ended in divorce in 1992. She made three solo albums before becoming a recluse on an island near Stockholm. Her daughter, Linda, has appeared in a musical written by her father (Bjorn) and Benny.

In a plotline straight out of a movie, she entered into a relationship with a stalker who had pestered her for years, only to have a restraining order placed on him when the affair ended. She makes very few public appearances -- and, as expected, did not turn up at the London premiere.

Meanwhile, the film's most bankable star, Meryl Streep, has admitted that her family could only take her ABBA renditions in small doses. The Oscar-winning actress -- who has four children with husband Donald J Gummer -- was banned from practising some of the classic hits which appear in the movie unless she locked herself away in her soundproof cupboard.

"I think I have sung all of these songs about 70,000 times -- starting in my closet, which was the only place my family would allow me to practise, all the way to Pinewood and Holland Park where we were living. But I never got sick of singing these songs -- you just cannot but be excited when it starts!"

Mamma Mia! -- The Movie opens nationwide on Thursday

At the time, their songs were dismissed as throwaway pop, but, with the benefit of hindsight, the songwriting genius of Bjorn Ulvaeus and Benny Andersson has become apparent. While none of their studio albums stands up as classics -- with the possible exception of 1977's Arrival -- the group's glut of brilliant singles continue to stand the test of time.

Dancing Queen: one of the best pop songs of all time, and a tune guaranteed to fill dancefloors, it benefits from a masterful studio production boasting a sound culled from the over-dubbing of 12 guitars.

SOS: those who were unconvinced by Eurovision-winning song Waterloo, had to eat their words with this piano-led masterpiece, which offered dark lyrics amid the bright melodies.

The Winner Takes It All: heartrendingly bittersweet lyrics, written by Bjorn and sung wonderfully by Agnetha, the song is a thinly disguised account of the pair's broken marriage.

Take A Chance On Me: a magnificent dancefloor number that sounds as fresh today as it did in disco's hey-day at the end of the 1970s.

Thank You For The Music: the song that works brilliantly in Mamma Mia!, the musical. It's a show-stopper extraordinarie.

Summer Night City: another disco classic that showed the Bee Gees, then lords of the dancefloor, that anything you guys can do, we can do better.

I Do, I Do, I Do, I Do, I Do: a song that fused 1970s pop with Swedish folk music, it betrays Benny and Bjorn's early folk roots.

Gimme, Gimme, Gimme: what woman can resist belting out the line about desiring a man after midnight?

I Have A Dream: even Westlife's egregious cover can't ruin the song's hymnal qualities and idealistic vision.

Waterloo: extraordinarily kitsch, but surprisingly durable. It's the song that made everything else possible, helping ABBA emerge from Sweden onto the world stage.

- John Meagher