Based on the Colby/Ramble interview the Frankie Howerd show filming began around 20th June, for which Ruth was absent and Penny present. So this pic is in line with Ruth not being in the group around this time, but Penny not making it onto TOTP.
Actually rereading the article, the above photos indicate three things
1) Ruth was absent early July as a result of her choreography work
2) This was probably the most likely show Penny would have been on TOTP if she had appeared, but she's not there
3) The two male dancers are not on this performance, even though a couple of weeks previously James Ramble said they regularly appeared on the show, which undermines his statement.
Heres a similar looking set (using triangles) for Alan Price, possibly from 26-6-69 (i cant find any another listed for around that time). 1969 seems like a particularly difficult year to find much for, although there is another one in the book with a mirrored background. Perhaps Penny was not on TOTP and they only used her for the Frankie Howerd bits?
Something i've only just realised these seem to be one of their standard costumes (as seen in Bucket T and others) but with the centre piece finally removed.
♥♥♥♥ Cherry, Louise, Patti and Ruth Alliance ♥♥♥♥. If there's a cure for this I don't want it.