I like what dewey02 wrote on the Hoffmann forum:
"All of George Martin's tracks and Beatle-related LPs are simply credited to the George Martin Orchestra but no individual members are ever listed.
This is true for George's United Artist releases, including
By Popular Demand - A Hard Days Night -UAL 3383 and UAS 6383
George Martin & his orchestra Play HELP!- UAL 3448
George Martin instrumentally salutes The Beatle Girls - UAL 3539 and UAS 6539
Off the Beatle Track -UAL 3377 and UAS 5377
While I'm sure he had some regulars that he used time and again, I would assume that these were simply studio musicians that were called in at the studio rate, and not a fixed orchestra or performing unit that would "go out on the road" so to speak. But I would guess that many of the musicians that played in the GM orchestra may also have been called in to provide instrumental backing on Beatles tracks. I don't have any source for this, but it would seem likely that George Martin would call on those people he'd worked with before and were most familiar to him when he needed some strings or brass or whatever to overdub on Beatles tracks. Watch the All You Need is Love video and I'd be willing to bet you will be seeing more than a few members of the George Martin orchestra."
This quote came from this thread:
http://forums.stevehoffman.tv/threa...-version-the-instrumental-songs.264516/page-2
Whoever the alto player was, he was probably just a damn good professional, who knew how to take care of business.