Mamma mia, here we go again as Abba fever is the name of the game

You don't often see huge, permanent, stand-alone museums dedicated to popular culture, but the usual rules don't apply to one particular Swedish pop machine. This May Abba: The Museum will open its doors in Stockholm; one million people are expected to visit during its first year in operation.

It's going to be Abba-tastic all during May. Agnetha Faltskog (eternally known as "the blonde one") will release her first solo album in a decade (and very good it reportedly is too). Stockholm- based Spotify, meanwhile is entering into a big partnership with Abba to mark the museum's opening and may well use the occasion to officially roll out its new player.

With all four band members fully behind the venture and set to attend the opening night and perhaps even play together for the first time in decades, it's expected that Abba: Gold (one of the bestselling albums of all time) will be back at the top of the charts once again.

Abba have already sold more than 400 million albums worldwide. More than 50 million people have seen the stage show Mamma Mia! ; the film version is the most successful musical film of all time.

The truth is that, contrary to appearances, Abba were never a pop band. Musicologists have long tried to break their code, but the analysis is usually fruitless as the band music defies the conventions of pop composition. The intro to the song Mamma Mia changes its rhythm on the wrong beat (most producers would have got them to do it again) and on Money, Money, Money one of the bars is in a very weird 9/16 time – which really shouldn't be allowed to happen.

The consensus seems to be that while most pop music runs away from anything with a classical music feel, Abba's work has deep classical music structures that go unnoticed because of the "chirpiness" of the melody lines. A song such as Lay All Your Love on Me is much more intricate and loaded with musical surprises than you would think. Lyrically, because English wasn't their first language, Abba got away with beautiful murder. "You can deny it" was rhymed with "oh so quiet", and they even got a rhyme out of "Glasgow" on Super Trouper .

But Abba were all about the performance too, and the museum (which is in a very beautiful part of Stockholm) reflects this. The band didn’t want any of the usual labels- on-glass-cabinets nonsense. Yes, they may be rebuilding the cottage on Viggso island (which was Abba Central, basically) within the museum, but most attention come May will be on the museum feature that allows you to virtually don Abba stage gear (sparkly dresses, flared trousers etc) and join a life- size hologram of the band for a song and a dance.

After all, without a song and a dance what are we?