As a point of interest I've dug out some examples of his work principally dealing with science fiction subjects, prior to, and during his Thunderbird work. Frank wasn't a fan of science fiction but you wouldn't know it by looking at his work.
As many of you will know, Frank spent a year working on the Eagle Dan Dare strip, starting at the end of 1959 when he, with assistance from artists, Don Harley and Bruce Cornwall finished off the Terra Nova story. This was followed by Trip To Trouble and Project Nimbus.
In 1963 he illustrated the second Brett Million story, The Ghost World in Boy's World comic.
In 1966 he began his stint on Thunderbirds, however he did find time to do illustrations on several of the front covers of TV 21 for the Captain Scarlet strip. This one from August 1968.
He also did the cover of the first issue of Joe 90 Top Secret at the beginning of 1969.
His drew his final Thunderbird strip in TV21 & Joe 90 comic beginning September, 1969. There were four installments with the last two drawn in black and white.
Of course, Frank is also remembered for his contribution to the Daily Mirror newspaper strip Garth, which he took over in 1971. These two examples are from the second story he illustrated called The Cloud of Balthus.
Frank sadly died in 1976, and for a man who wasn't particularly keen on science fiction I wonder what he'd think about being best remembered for illustrating some of the best British sci-fi comic strips!