Catweazle's pet toad/familiar was called Touchwood.
The jaunty theme was actually a library piece called "Busy Boy" by Ted Dicks.
Geoffrey Bayldon had turned down the role of "Doctor Who" (1963-present) resulting in William Hartnell being cast. He later said he regretted his decision as the show became hugely popular with children. Not wanting to repeat the same mistake he was elated when he was offered the role of Catweazle.
Not all of Catweazle's sayings were gibberish. Richard Carpenter did some research into medieval times and used some genuine apothecary spells and some old Hebrew to make the language more authentic.