Great pictures, Mikey. The girl is either Diane South - then it would be an image of the Beat Girls - or Felicity Balfour - early Pan's People. Unfortunately there are hardly any other pictures of those two. On page 31 in the book, you can view a picture of the Beat Girls with Diane South. In my humble opinion she doesn't look like the girl on the pictures you posted but I could be wrong. I think Diane is on the pic on page 23 as well (right next to Flick).
So I guess the girl behind Babs is probably Felicity Balfour, and those are very early Pan's People images.
On Pg 45 of the book, Dee Dee speaks of Penny Fergusson "a sultry sexy girl with ginger hair" Could it be Ruth behind Babs and Penny front right (it looks like her from the pic on Pg 36) or am I crazy arguing with a couple of Ruth fans like this? The book also says that Ruth replaced Felicity Balfour in early Pans BTW.
Some Dancers who gave a good time, broke all the rules, played all the fools, yeah yeah yeah they blew our minds