London's New Scene: Art and Culture in the 1960s by Lisa Tickner just arrived.
414 large pages, heavily illustrated, this is a comprehensive book on 60s art. The first chapter (35 pages) cover Ken's Pop Goes the Easel others cover sculpture, the art school revolution and photography making use of Antonio's film Blow Up.
I have skimmed the book (in the hour after it arrived!).
The introduction is thoughtful, and also brings in Ken's London Moods, with a good 1966 photo of Ken. It quotes photographer Lord Snowdon on the film "really marvellous and tremendously exciting".
On Pop Goes the Easel it mentions Ken approached Hockney to appear as one of the artists in the film, but Hockney refused "Hockney did not see himself as part of a group or having a significant connection to Pop".
The book quotes Michael Brooke comparing Ken's "elaborate, rapidly-cut rhythmic kaleidoscope of images" to Jean-Luc Goddard "though Russell had arguably gone further by 1962".
In the later section on Blow-Up by Antonioni there is a quote by Melvyn Bragg "There is no doubt that Antonioni lifted his famous 'blow-up' sequence from the central section of Ken's film [Watch the Birdie]".
This is all from a quick skim of the book!