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I'm just watching this on Crackle tonight - it's been many years since I saw it. This time I was noticing a LOT of tuba playing for the comic character and scenes. As near as I can tell, it was the LSO playing on the soundtrack, which would make me think "John Fletcher," but he joined them a couple years later. Also, I'm not 100% sure it's a tuba. If so it's a small one (Besson F perhaps), but it could be a tubist playing euphonium with a larger mouthpiece.

Does anyone know who was playing and what the instrument was?