Put the question out over at the Bootlegzone Forum and i got a reply from John C Winn none the less.
He pointed me to Michael Braun's Love Me Do book, which was his source.
On page 103 Braun writes
"The Beatles, with Aspinall standing in for George, rehearsed only for camera angles and whispered their songs. This was rather disappointing for Kathy and Nancy Cronkite - the daughters of the CBS newsman, Walter Cronkite - who had been admitted to the the studio to watch the rehearsal. . . Towards the end of the afternoon George turned up ...