Via the Zombies Fan Club on Facebook, here's
a link to a page on Russ Ballard's website of an Argent concert from 1971. The data from the Facebook post give only the year and that it was probably recorded from the radio on Sunday. I did some research and discovered the exact date: 14 February 1971. In the audio file itself, the announcer (identified as John Peel in the Facebook post) mentions that a band called Egg played the first half and that next week's program will feature the Roy Young Band. There's a wiki devoted to Peel's radio broadcasts, and
the page for 1971 lists a program with Egg and Argent on 14 February 1971 and a program with the Roy Young Band the following week (21 February).
The specific page for 14 February 1971 links to
an archived version of a BBC site with details on the Egg recording, including the location of Lower Regent Street, which Ballard confirms in the Facebook post: "I remember the show, it was recorded at the BBC Regent Street."
Here's the set list:
- "Lothlorien"
- "Chained"
- "Rejoice"
- "The Fakir"
- "Sweet Mary"
After that, the tape seems to skip, and there are additional, different versions of "Rejoice" and "Chained." Those don't seem to be from the same show, since Peel says, "Argent finish with 'Sweet Mary.'"