About halfway through, a musical passage/fragment depicted the rising paranoia of an older lover getting overcome by suspicion over a younger love object, and it sounded VERY familiar.
Movie and soundtrack composers are often asked to write something obvious or overt for certain scenes by the director.
Certain tonalities have been pegged with certain emotions after their repeated pairing in movies. (Major = lightness, joy Minor=pathos Whole Tone= trances, dreams Diminished= fear, paranoia)
It's possible that the similarity you hear may simply be a result of similar harmony and rhythmic devices being used by both composers.
After awhile of trying to place where I had heard something very similar before, I am fairly convinced that it was from Funny Thing, not one of the songs, more like an instrumental/mood passage, where the vestal virgins were doing their frenzy thing.
I have ZERO idea whether this is anything more than coincidence. It could be an inside-baseball reference or tribute; it could be screen composers linked somehow; it could be a sly reference to "Rome" or the underside of love in both features; or it could be plagiarism or NOTHING.
This is also possible. Both composers could be quoting a bit of a famous classical work as an homage.
From the clues you've supplied, some quotable possibilities that come to mind would be Stravinsky's Rite of Spring (you mention the vestal virgin frenzy and spring appears in the title of of the Helen Mirren movie)
Or, the music could be a snippet of something from Respighi's Roman trilogy (three famous symphonic poems- The Pines of Rome, The Fountains of Rome, and Roman Festivals)
Sondheim, Ken Thorne (who supplied some of A Funny Thing's incidental music), and Richard Addinsell would all be quite familiar with those famous pieces.
If you feel like pursuing this further Mrs. Stone is on YouTube in 8 parts.
Part 1
http://www.youtube.com/watch?v=h6IbMgCjZ40Part 2
http://www.youtube.com/watch?v=GQ97ro0GpFY&feature=relatedetcetra...
If you can find the exact music for me to listen to, I may be able to identify it.