He wrote "Alexander the Mouse", a story about a mouse born to be king. Using an Irish-produced magnetic system—on which animated characters were magnetically attached to a painted background, then filmed using a 45 degree mirror—he persuaded Peter Firmin, who was then teaching at the Central School of Art, to create the painted backgrounds. Postgate later recalled that they broadcast around 26 of these programmes live-to-air, a task made harder by the production problems encountered by the use and restrictions of using magnets.