On this day, The Beatles visited Twickenham Film Studios to film their only real appearance in the Yellow Submarine film (the end bit). They were also filmed doing a variety of other activities. One of these activities was Paul recording or mixing something. As in these photos, he is seen working with a 4-track mixer and a Nagra recorder. None of the references seem to indicate exactly what it is that Paul is doing nor does any reference indicate who the two women are. It seems logical that it would have something to do with the Yellow Submarine film.
Excerpts of Paul's session were seen in The Mod Odyssey and a Yellow Submarine trailor.