I fail to see how Eric Siday's nationality matters.
Nationality makes no difference (this wasn't the point).
Turns out that there are in fact two authors of the Screen Gems Logo, the other being Van Alexander (one of Screen Gems sixties in-house composers). I suspect Van contributed the muted trumpet fanfare bit at the end so the thing had a more regal "Hollywood-type" sound (Screen Gems, after all, being the television "arm" of Columbia Pictures) and didn't sound too much like a variation of the NBC "Chimes" ID. Still it was quite the change from what Frank DeVol had composed two or so years earlier.
FYI - Siday settled in America while in his mid-twenties, a naturalized citizen.
Thanks to all for the interesting info and observations so far. Any more comments on the album itself and the "truncated" (my controversial inverted commas) career of Arthur Morton as composer? Or even Alexander Courage?