I don't know what the theme to Steptoe
and Son is (was that the British predecessor to Sanford & Son?) but
the legend I had heard was that someone was trying to tell the band
about Love's version of Little Red Book (by Bacharach) and hummed the
melody. Syd began playing it on the guitar and it morphed into the
Interstellar Overdrive riff. It seems unlikely but actually makes a
bit of sense if you hum Little Red Book kind of slowly.

It was Floyd co-manager Peter Jenner. I would trust his account.
(Mark Steven Brooks/Elaterium Music)