Television is taking over from teachers according to research commissioned by the makers of Screenblock, a device that limits the amount of time kids can spend in front of the box. It found that children were spending almost twice as long staring at the screen than they were learning in school — for every hour spent in the classroom, 1 hour 40 minutes was spent watching telly.

Spread across a whole year, that means that children are spending 58 days glued to the set and playing computer games, or an average of 3.8 hours every day, as opposed to 2.3 hours a day and 35 days per year in school lessons.

Naturally, Screenblock's makers had an ulterior motive for commissioning the survey, which looked at the viewing habits of over 500 British families, as the device is aimed at parents who are worried about the amount of time their kids are spending watching TV.

Screenblock plugs directly into your TV set, controlling its power supply, so parents can have control over how many hours it stays on. Children are given a prearranged time limit, and once it is up the television simply switches off. Children can bank their television time, saving it up to view the programmes they most want to see.

The device is controlled by a parent key to make it child-proof. Parents can also use a disciplinary red and yellow card feature that allows them to cut or extend viewing time depending on a child's behaviour. For example, a red card instantly switches the TV off, while a yellow card reduces the daily allowance to 15 minutes. But a blue card is also available as a reward, extending daily viewing by an hour.

Its developer, Tony Ratcliffe, came up with the idea when he realised that his own two children were spending too much time in front of the TV and it was making them moody, inattentive and inactive.

Screenblock goes on sale today priced £79 ex VAT, and can be purchased at the website, or by calling 0800 028 2212.