In the Look and Read series Sky Hunter (1978), Geoffrey Bayldon plays Mr Trim - or rather, he actually plays Doctor Who, doing a note-perfect imitation of William Hartnell's performance!
Look and Read is intended for seven-to-nine-year-olds, so the audience wouldn't have been familiar with William Hartnell's era, but the director and actor very clearly were! Apparently the Doctor Who team were considering him to play the First Doctor in The Five Doctors in 1983, but John Nathan-Turner thought he'd be too familiar to viewers from Catweazle and Worzel Gummidge - which I think is a great loss to the series, with all respect to Richard Hurndall.
I definitely watched at least one episode of Sky Hunter, even though I was below the target age when it stopped being shown - I distinctly remember the "Welsh telegram" episode, which I quite probably saw in the autumn half-term immediately after my sixth birthday. I don't recollect anything about Geoffrey Bayldon's role in it, though, so it was a great delight to watch it today and see him.
Really, he should have been the First Doctor. I mean, they let Jon Pertwee be in it, even despite Worzel Gummidge!