The Beatles were keen to make a guest appearance. The band had been regulars at the Riverside studio, but their timetable and that of the Doctor Who team never quite meshed (though there are photos of John Lennon apparently asking a Dalek for an autograph). The original script [of "The Chase"] was about the fiftieth anniversary of their TV debut, a concert in 2012, and the Beatles were to have been made up as old men. Later drafts said that it was 1994, and that they were appearing on 3D BBC-TV in colour. Some reports have hinted that their manager, Brian Epstein, vetoed this for his own reasons, but quite simply it was a logistical non-starter. On the day that pre-filming for episode one took place -- the 12th of April, 1965 -- the boys were seven weeks into filming Help! and needed to come up with a song to fit the film's new title. Tuesday the 13th saw them back at Abbey Road to record "Help!," which had been rush-written that weekend.
Plan B was to use a clip of the Beatles on Top of the Pops, but the Doctor Who production team discovered that each edition was wiped after broadcast. Only six exist for the whole of the 1960s, and even these are fragmentary. Plan C was for the Beatles to come into Riverside (Saturday the 10th of April, so pretty close to the wire), and make a clip for TotP, one minute of which was transferred onto VT for special use in Doctor Who.