The Abba girls given lessons in singing without accent

Unlikely. They would have had help with pronunciation perhaps, but that would be it. Accents don’t tend to come out in singing and, if they do, it’s deliberate (the Scottish act The Proclaimers springs to mind - so determined were they to put their accents in their singing, what came out was arguably barely singing at all). British acts would sometimes put on a slight American accent in order to appeal to the US market.

However, there are some exceptions. The English version of Waterloo has them barely pronouncing the “t” in the title, in a more American way. In the Swedish version, the “t” is very clear.

In later years, it would appear they took less interest in correct pronunciation, hence Agnetha’s hard “Champagne” in Happy New Year.

I agree with Alan - it's very unlikely that the girls took such lessons; it's more likely that they might have occasionally been given guidance in the studio on certain words - for example, from Björn, whose command of English was just that little bit more assured for most of the period when the group recorded together.

And some of the Swedish pronunciation can be quite charming, in my view - for example, the hard 's' that Agnetha sings in 'I apologise...' in 'The Winner Takes It All'.

Some instances do, though, grate a little with me - such as the aforementioned 'Champagne' in 'Happy New Year'; I do wonder why the line wasn't corrected. And Agnetha also appears to struggle with the word 'wound' in 'Disillusion', although I think that song was recorded in a rush and perhaps it wasn't noticed or they felt it didn't matter....these are mis-pronounciations rather than accent issues, of course....

I like their accented singing, too. It's more authentic than that fake mid-Atlantic thing that so many singers do. I've noticed Frida's accent too, Josef. I suspect it is her original Swedish accent, flavoured by the local Swiss dialect, topped up with the likely influence of a posh British boyfriend. They say that musical people tend to pick up accents more easily?

In fact, I think it's the opposite: she tried too hard to pronounce it correctly, thereby making the mistake. The 'ch'-sound in 'champagne' sounds more or less the same in Swedish, English and the original French. It's a case of what linguists call 'hypercorrection'.