Yes, Jet Starr is Yaroslav Horak.
However, when I first looked at the book, I was put in mind of Paul Norris's work on Brick Bradford, quite popular about that time. Many of the design elements and costumes perhaps indicate Norris was an influence.
I mostly associate Horak with his James Bond albums, and as you can see, by that time, his work had changed and matured considerably.
Yaroslav Horak on James Bond
https://davekarlenoriginalartblog.blogspot.com/2008/08/yaroslav-horak-on-james-bond.html
Beautiful work - which, now i see it that way, really needs to be blown up big to fully appreciate.
Paw, I can see why you are enthusiastic about these collections.
Cheers!
Link to the book:
Chris Welkin Planeteer