ABBA won the award for "most popular artists of 1977" as voted for by readers of The Sun newspaper in this awards show hosted by Dickie Davies.

The late TV presenter Russell Harty (who interviewed Frida on his talkshow Harty in 1983 and Björn and Tim Rice on Harty in 1984) went to Stockholm and was seen outside Glen Studios. Snow was on the ground and it was dark. Russell spoke to the camera and said something like, "Inside ABBA are recording their latest hit and I'm about to go in and surprise them with their award."

You could hear Take A Chance On Me outside and Russell went in to the studios with ABBA pretending to look surprised and stopped singing - as they pretended to record. Russell handed over the award to them.

The picture above is from a newspaper cutting, the text of which reads:

"This was the third year running ABBA won this award.

Benny: "We are delighted to have won again, we treasure our Sun awards. We know we must be doing something right when all the readers of The Sun approve of us."

Bjorn: "Winning a television award means a lot to us, because we are always rather reluctant to appear on television. We always feel it is difficult to transfer our music to TV, and almost impossible to reproduce our recorded sound."

See a picture of ABBA on the same day here.

Thanks very much to Richard Knight's fantastic memory for this information!
Thanks also to Michael Price for the newspaper picture and the related quotes from the paper.
Extra thanks to Carl Magnus Palm and to Matt Hayes for clarification.