Abba are not sure if their new songs are ''good''.

The 'Dancing Queen' hitmakers - comprised of Agnetha Faltskog, BJORN ULVAEUS, BENNY ANDERSSON and Frida Lyngstad - revealed last week they had been secretly working on two new tracks to release in conjunction with their planned digital tour, and though they only wanted to release the songs if they met a certains standard, they still don't know if they've reached that.

Benny said: ''We never said we wouldn't reunite in the studio -- we said we wouldn't reunite on tour and we have this digital tour and thought it would be nice to have a couple of new songs in there.

''We said, 'Let's try and see what happens and if we don't think it's good enough we won't release it and if we think it is good enough we will.' We still don't know if they are good -- but we didn't know that when we released the other tracks either.

''One of the songs is like we would have written it for today. The other, we could have written in 1972. So I don't know, we'll see. I mean, they're not finished yet.''

Despite their past chart success, the quartet aren't worried about whether or not comeback single 'I Still Have Faith In You' will reach number one.

Bjorn insisted to The Sun newspaper: ''We don't worry about that. We're just having fun.''

Though they've only been working on two songs, the 'Mamma Mia' singers teased there could be more to come.

Asked if there'll be other tracks, Bjorn said: ''Who knows? Just never a tour.''

The 'Waterloo' hitmakers - who shot to fame after winning 'The Eurovision Contest' in 1974 - have been turned into 'Abbatars' for a digital tour which is being lined up for 2019 or the year after.

Talking about the process of making the holograms, Bjorn said previously: ''They photographed us from all possible angles, they made us grimace in front of cameras, they painted dots on our faces, they measured our heads.

''Apparently a cranium doesn't change with age the way the rest of your body falls apart.''

In June 2016, the 'Winner Takes It All' group made a rare appearance together, marking the 50th anniversary of Benny and Bjorn's first meeting at a private party at the Berns Salonger hotel in Stockholm.

However, though the foursome appeared on stage, only Agnetha and Frida sang, treating guests to a rendition of 'The Way Old Friends Do'.

Prior to that they came together for the opening of Stockholm's 'Mama Mia! The Party', which was held on January 20, but they didn't perform on that occasion.

The band's last album was 1981's 'The Visitors'.