The TV news showed a report on ABBA as they were performing in concert at the Brøndbyhallen in Copenhagen.

The reporter claimed that had tried their best to broadcast direct from the concert hall but were not allowed, so instead footage of the outside of the concert hall and the entrance hall were shown along with a small interview with Stig and old footage of ABBA.

ABBA could be heard faintly in the background.

However, it's doubtful that it was broadcast the same night as it was filmed.  In a Danish weekly it said that the producer, Mogens Berendt, almost wasn’t granted permission to broadcast the clip, although it had originally been OD'd, because Stig/ABBA were afraid of over-exposure. Knud Thorbjørnsen, who promoted the Danish ABBA show, had to call Stig from from his holiday in Barbados to convince him to grant permission.

Also, according to the article this clip was not used in TV-Avisen, but in TV-Aktuelt (* needs clarification), as part of a report entitled Agenten (“The Agent”), about managers and agents such as Knud Thorbjørnsen and others. According to the story, the ABBA clip was “very recent”, so the broadcast was probably sometime in February. It also says that it was broadcast on a Tuesday.

It could be that the clip was used in other contexts as well, prior to the broadcast of this Agenten report, but either way it couldn’t very well have been broadcast at 7pm on the very night of the first concert, since the concert had likely only just started at that time. The article also doesn’t say if the clip was filmed on 31 January or 1 February, the date of their second Copenhagen show.

TV-Avisen, 1977;
TV-Avisen (Benny & Björn), 1995;

Thanks to Jan Bach's amazing memory!  Extra thanks to Mean Mr Wallis and Carl Magnus Palm.