This has happened before - when Getty saw English pop star Fatboy Slim's album cover "Halfway Between..." (sunset between legs) and thought it looked like "Sunset Silhouette" by Ernst Haas. After checking the ip addresses of visitors to their website they proved that his album cover was inspired by their photo and so got compensation.
It doesn't matter how similar Fielder's photo is to previous photos because he did not copy them.
It doesn't matter how different Houghton's is from Fielder's because he did copy some of it.
(This is not like patenting inventions, where only the first inventor can get (and keep) a patent).
The judge said Houghton could have got an independent photographer who had not seen the original to provide a photograph of a red bus on the bridge with Parliament and Big Ben.
(This is similar to how IBM PC's (the BIOS), were cloned, they had programmers in one lab analysing the code and passing instructions to programmers in another lab who were not allowed to see the original.)
DUMB4SS: The court even admitted that the defendant had gone out of his way to avoid infringing the copyright of the claimant.
Fairly ridiculous as with a quick google image search, I found at least another 8 different images showing a red London bus in front of a BW Houses of Parliament.
Not from 1957, but 1957 is part of the title of the photo as its in the style of 1957.
A red bus or a red telephone box in London with the rest monochrome is an old cliche. (pun). I can find hundreds of such images on the web:-.
Red bus + big ben B&W. http://www.maidenhead.cc/bin/view/Main/CompImages2009to10A
London Bus by Ingrid Gledhill (2009)
Maybe it's so expensive so that they don't actually have to make one.