This has been debated at some length at various times on the AB.
Some people believe that any piece of prommo. film counts as a video, but to be strictly honest, the first film made specifically by a band to promote a single was Queen's 'Bohemian Rhapsody'.
On this occasion, the band knew that their single had climbed the chart, and they were due to appear on TOTP, but they were touring, so they specifically filmed a video to be shown in their absence.
So, strictly speaking, this the first pop video on TOTP - it was not a piece of prommo, film, it was a specifically designed video made to be played in the absence of the band, and that, many believe, makes it the first 'pop video', but as before, this is open to debate.