Premise: The Kestrels were a vocal harmony quartet from Bristol, England, most notable as the group through which the songwriting team of Roger Cook and Roger Greenaway first met and started composing jointly. They were one of the busiest vocal groups in England during the late 1950s and early 1960s, singing back-up behind Joe Brown, Billy Fury, Eden Kane, and Benny Hill, amongst others, and made dozens of television appearances between 1958 and 1964.
Hypothesis: The Kestrels sang back-up behind several people.