Alexander is right about the Overture's being a fully symphonic treatment of the Marcus and Lygia theme; it was also used as the Exit Music ("Epilogue" on the Decca/London Phase 4 album).

Mark Koldys has a tape of the original tracks to this cue.

And I, too, share a certain fascination with the relentlessly Erotic Miss Laffan. Hers are among the best scenes in the film, especially her reactions as Peter Ustinov's Nero commences to sing.