Do you mean the programmes or the advert Dot?
I know the programme was well before my time, but i thought the advert was more recent.
The one where the narrator says to Windy Miller that if he eats a bowl of this cereal every day, he can get lots of energy to run.
Windy frowns at this suggestion and shakes his head,
and then an attractive female (not sure which character this was) jogs past, and he quickly nodds and jogs off after her!
One of the less well known characters is Mr Dagenham the salesman. He drives a red car and tries to sell Windy Miller something, I think maybe a helicopter??His song is "he can sell anything, anything money can buy" and featured in one episode of Camberwick Green. Although many of the characters only came up on the music box once, for a story about them, some characters feature in many other programmes or are just better remembered.