The government's TV advertisements promoting adult learning have been judged too frightening to be shown before 7.30pm.
Following 13 complaints, the Independent Television Commission has ruled that the adverts, which feature green gremlins, must not be shown when children are likely to be watching.
The ITC upheld complaints about the advert earlier this year and the department of education re-edited the adverts, but the watchdog has said even the milder version is unacceptable during daytime TV.
The ads feature a small, green, human-type figure with pointed ears dressed in a boilersuit, who pops up and taunts an embarrassed adult about their reading skills.
The gremlin figure is played by actor Warwick Davis, who has played leprechauns and midgets and has starred as Yoda the Ewok in Star Wars and as Professor Flitwick in the Harry Potter films.
Viewers complained that children aged up to five had been frightened by the ads after seeing them during the daytime and early evening. Several had experienced bad dreams and sleepless nights.
The ads by the Department for Education and Skills, aimed at promoting adult literacy, urge them to overcome their personal "gremlins" at reading and writing.
In one advertisement a gremlin took the receiver from a woman's hand as she was making a telephone call and then ran his fingers menacingly over her hand.
The government said 470,000 people have signed up to courses since the ads were first shown.
It ruled the elements of "tension and shock" in the ads were too strong to be shown any earlier.
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