Matt -
I also bought Hasbro's Chain Letters to see if it had any elements of the old Hatos-Hall show. Interesting that the Hasbro game box credits includes one for Schnur- Appel. Wonder if it's connected to former GT producer Jerome Schnur, who ghost produced Jack Barry's "Everybody's Talking"? Anyway, the game is completely different. The game description is in the UK Game Show page. 3 players compete for high score after three rounds of play involving words of four letters.
Round 1: Players get a starter word, then race to be the first to make 20 new words by changing one letter each time. If my word was WIRE, I would go: FIRE, FARE, HARE, HART, PART, MART, MARK, DARK, and so on. No repeats. The timed round ends when one player reaches 20 or all players are beat by the clock. Any incorrect words cost you points.
Round 2: Booby Trap - You get a base word, like GOOD. You have three chances to score on your turn by changing one letter in the same base word. The opponents try to anticipate a word you may choose and write it down. Say my booby trap word was "gold". If you change the word the first time to HOOD, you score. If you choose to double, you might play GOOF. If you want to risk a third try for 4X - if you wrote FOOD, you'd win it all. If you chose GOLD, I gotcha and get the points.
Round 3: Players make a chain of words your opponents get to guess. If the start word was WARN, I come up with a word, then give you clues. I might first say, "change the N" and my clue would be "adoptee". If you guessed by word was WARD, you'd score, then you'd come up with a new word for the next player. If no one can guess your word, you keep the points. Words may be expanded to 5 letters in this round, but no less than 4.
High score at the end wins.
This would be a tough sell in the US, but I could see it in the UK. The game was made by Spear's Games (a division of Mattel now) in 1990.